Both Blackwater Creek and the Wekiva River are entwined into my personal history. Let me begin with Blackwater Creek. I will get to the Wekiva later in this text. I remember in the early seventies paddling Blackwater creek from the bridge at Lake Norris Road, just south of the headwaters, to SR44—a trip of only about 5 miles. We spent most of our time pulling our canoe over logs, and pushing through water hyacinths. It took about 12 hours. I do not think many people have actually made that trip, and I do not believe it is allowed today. The section of Blackwater Creek from Lake Norris Road north to Lake Norris has been opened by the SJRWMD. Before this section of the creek was purchased by SJRWMD, it was very difficult to get to Lake Norris because of the water hyacinth mats  that clogged the small creek channel. The hyacinths have since been removed, and the SJRWMD also clears away logs which cross the channel, so the paddle now is comparatively easy.

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I am not certain about the extent to which herbicide spraying occurs within this section of Blackwater Creek or Lake Norris, but I have never seen airboats in the lake or any evidence of spraying. Most of the aquatic plants within Lake Norris are either what we call bonnets, or spatterdock (Nuphar luteum), other water lilies (Nymphaea sp.) and what I believe is giant bulrush (previously Scirpus californicus now Schoeneoplectus californicus). The submerged aquatic plant community, which is sparse, appears to me to be dominated by southern naiad (Najas guadalupensis) in the proximity of the shore. A few stands of cattails can also be seen around the lake. There are occasional groups of water hyacinth and alligator weed, both showing signs of attack from the weevils and other beetles brought in as biological controls. Since the Conservation Area was established, I have never seen these two invasive aquatic plants reach populations which could be considered extensive, although the Florida Fish and Wildlife Commission (FWC) in their 2015-2016 annual report did note that 21.4 acres, or about two percent of the lake area was sprayed for floating aquatic plants (water hyacinth probably). I have never seen any indication of hydrilla in the lake, nor was there any record of spraying for hydrilla in 2015-2016 in Lake Norris.

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When you look at the roots of the water hyacinths from Lake Norris/Blackwater Creek, they are noticeably long, indicating a relative scarcity of at least one essential nutrient. A quick glance at what water quality monitoring has been conducted on the lake indicates this scarce essential nutrient may be phosphorus, which is typical of many lakes in central Florida.  The relative abundance of the major nutrients-- phosphorus, nitrogen and carbon--have a significant influence upon the rate at which aquatic organisms—including aquatic plants and algae-- grow and expand, at least to the point that space becomes limiting. Biologists have known this since the 1800s, and have modeled many biological systems—including biological wastewater treatment systems-- based upon this realization[1].

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In 1977, two South African biologists, C.F. Musil and C.M. Breen[2], made an assessment of the growth dynamics of water hyacinths on a nutrient-laden lake when considering the possibility of removing nutrients through water hyacinth cultivation and periodic removal through mechanical harvesting[3]. In their evaluation they applied a technique known as the Lineweaver-Burke[4] method for estimating the maximum growth rate (µmax) for water hyacinth and the concentration of phosphorus needed to realize a growth rate of one-half of this maximum rate (Ks).  To avoid putting the readers to sleep, I will not get into the details of the Lineweaver-Burke method or other considerations related to determining the rate and extent of water hyacinth growth. If you are interested in such detail, I suggest a text written by Patrick Brezonik who was at one time a professor at the University of Florida[5] or a paper in which I was involved regarding development and application of a practical model related to cultivating water hyacinths for nutrient removal and recovery[6].

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Inspired by the work of Musil and Breen, and by serious researchers and practitioners such as those with NASA in Bay St. Louis, Mississippi[7] and Agricultural Engineers at the University of Florida [8] and others, in the mid-seventies I chose to pursue the possibility of applying aquatic plant cultivation for nutrient removal and recovery from wastewater and impaired surface waters. Over a period of forty years, this effort resulted in the development and application of the concept of Managed Aquatic Plant Systems (MAPS), which was presented and offered in recent Blogs as a practical nutrient removal and recovery strategy for the Kissimmee-Okeechobee-Everglades Ecological Amalgamation or KOEEA. See:                                                                                                                        

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Shorter roots on water hyacinths as shown on left, with plants from the Lake Okeechobee Basin with higher phosphorus levels as compared to the longer roots from Lake Norris/Blackwater Creek with lower phosphorus levels in the middle picture. Scars from the water hyacinth weevil, Neochetina sp. noted on leaves of plants from Blackwater Creek on the right.

 

 

Why am I telling you all of this? Well let me just give an example of what all of this research and development has taught us. Let’s go back to the Lake Norris situation. Records indicate that the concentration of total phosphorus in the lake averages somewhere around 60-80 micrograms per liter of water, or µg/L, or as often reported, parts per billion or ppb. Presently, total phosphorus in Lake Okeechobee is at about 150 ppb, and lakes such as Lake Apopka are closer to 200 ppb. The Everglades limit you might recall is 10 ppb. Perhaps you look at these numbers and think--“so the phosphorus concentrations from Lake Norris to Lake Okeechobee are about doubled, so what!”

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This is where science becomes helpful, so let me put this in perspective. How do these concentration increases impact growth rate and the extent of coverage over time? Well, based upon previous research, including the work by Musil and Breen, it is recognized that water hyacinths have the capability of growing at a maximum rate of about 4% each day, and that at total phosphorus concentrations of about 270 ppb, when all other factors such as nitrogen, carbon as atmospheric carbon dioxide, sunlight and temperature are at optimal levels, will be at about 2% each day. When we apply the four total phosphorus concentrations cited to the growth models—10 ppb for the Everglades, 80 ppb for Lake Norris, 150 ppb for Lake Okeechobee, and 200 ppb for Lake Apopka—we find field growth rates are 0.14% each day for the Everglades; 0.91% each day for Lake Norris; 1.43% each day for Lake Okeechobee; and 1.70% each day for Lake Apopka respectively. Perhaps you might think this range is not that great. But think of these rates as similar to compound interest rates—you all know what happens to your mortgage payments when interest rates increase by just fractions of a point. And remember growth rates are on a daily basis, not in monthly allocations as with annual mortgage rates, so compounding is applied to each day. So what does this look like? 

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Well here comes the shocker! And please look at the graph in Figure 1, as you read this. If we start with one acre of water hyacinths, after one year, at 10 ppb total phosphorus (Everglades) the acres covered would increase only to 1.70 acres[9]. If the total phosphorus were 80 ppb (Lake Norris) the hyacinths would at the end of a year cover about 29 acres. Now consider the Lake Okeechobee situation at 150 ppb. By the end of one year the coverage would be nearly 198 acres, and when we consider 200 ppb total phosphorus as with Lake Apopka the acreage at the end of one year will be close to 548 acres!! This means when the total phosphorus increases by a factor of 2.5 from Lake Norris conditions to Lake Apopka conditions, the coverage increases by almost 20 times or 2,000%. And with an increase from Lake Okeechobee conditions of 150 ppb total phosphorus to Lake Apopka conditions of 200 ppb total phosphorus—an increase of only 33%--the coverage increase is nearly 300%. This is the reality of exponential relationships. It is no wonder we have massive problems with aquatic plant growth in many of our nutrient impaired lakes and rivers! We have been dumping huge amounts of nutrients into our waters—either directly through discharge or indirectly through runoff and seepage—since the turn of the nineteenth century.     

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 Figure 1: Growth Dynamics of water hyacinth as influenced by total phosphorus concentrations.

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It is commonly believed that water hyacinths were released into Florida waters sometime around 1884. Originally thought of as a decorative ornamental plant, it did not take long to spread throughout Florida’s freshwaters, becoming a problem for navigation, flood control, fishing and general use of water resources. When hyacinths completely cover a water body, oxygen transfer to the underlying water is significantly reduced, and the heavy vegetative cover soon promotes development of tussocks and the accumulation of organic sediment.

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Water hyacinth which is native to South America was introduced to Florida without any of its attendant native diseases, pests or grazers. With its naturally high growth rate, and without the encumbrances of diseases or pests, water hyacinths flourished in Florida’s waters, particularly those which received large amount of nutrients, such as Lake Apopka and Lake Okeechobee. In response, the herbicide application industry was born. And while water hyacinths and other invasive plants such as alligator weed and hydrilla have been controlled to some extent through the introduction of native pests and grazers such as the hyacinth weevil, the flea beetle, and the grass carp, I believe the use of herbicides remains the primary means of destroying expansive growths of these and other invasive plants. Comparatively little has been done by involved agencies and academic research centers to develop and refine cultivation or mechanical harvesting technologies.

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Over the past decade the use of herbicides has become controversial, and battle lines have been forming on both sides of the argument. It is difficult to find fault with the early use of herbicides when massive expanses of water hyacinths overwhelmed many of Florida’s water bodies, or when the submerged exotic plant hydrilla began to “top out” and impose upon the ecological stability of many cherished lakes, streams and rivers. But there is always the other side of the coin.

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Water hyacinth roots, for example, can provide valuable habitat for many aquatic species such as small crustaceans, amphibians such as sirens and tadpoles, and even other vertebrates such as the Black Swamp Snake and the pygmy sunfish, while the shoots offer food or refuge or both for many animals such as the diving spider, the red bellied slider and the purple gallinule. Hyacinths also provide respite from the sun for sports fish such as the largemouth bass.  In addition, they can shade out algae responsible for Harmful Algae Blooms (HAB); can facilitate nitrification of toxic ammonia nitrogen; can produce usable protein at a rate over 10 times that of wheat or soybeans, and can even produce natural algaecides called allelopaths which can interfere with the growth of harmful algae including cyanobacteria.  Similarly, hydrilla can also restrict algal growth through shading, competition for nutrients, and possibly allelopathy. Hydrilla at modest levels can also generate a net oxygen gain in the water, and create a habitat for many aquatic species.

 

I have talked to fishermen who find fishing often best around small hydrilla and water hyacinth patches, and I have experienced this myself.  Therefore, it makes sense that we look at both perspectives. As with so many situations, moderation appears the best alternative. So, let’s consider what a strategy of moderation might look like.

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The other day I put my kayak in at Katie’s Landing off Wekiva River Road, a couple miles north of SR 46 on the Seminole County side of the Wekiva River. Every time I come here, I am reminded of Katie and Russ Moncrief who owned this site and ran it as a place for people to rent canoes and enjoy the river. It is now a state park. Russ and Katie were among the Founders of the Friends of The Wekiva River, which was started in 1982 by Russ Fisher, and supported by many skilled and enthusiastic founders such as Fred and Pat Harden, Jim Hulbert, and Jim Thomas. I was lucky enough to have been asked by Russ Fisher to join the Founders, although my contributions were quite minor when compared to the others. Under the effective leadership of Russ Fisher, the Friends were able to make significant progress in protecting the river, including securing a designation as an Outstanding Florida Water. The Friends of Wekiva River are still active and Katie Moncrief is listed as an Emeritus Board Member. The river has changed some since those days, but it is, thanks largely to the Friends, still a beautiful place.

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As I moved my kayak northward from Katie’s Landing I would occasional throw a small “beetlespin” around the logs and small patches of aquatic plants.  Typically I would catch redbreast sunfish, specks or an occassional stumpknocker. I am always impressed by the intricacies of the coloration of these fish, and I often take a picture before releasing them. On occasion, when I moved the lure a bit slower, I would catch a shellcracker. And, of course there were usually many small bass hanging out around shade protected eddies.

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This speck (which was released) is typical of what I catch on the Wekiva River and Lake Norris. However, in areas such as that shown in the picture of the Wekiva River to the right,  where recent herbicide spraying creates mats of dead and dying vegetation, I rarely catch any fish. Photos by Allen Stewart

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On this day after being on the water about fifteen minutes, I began to notice dead spots among the aquatic plants (see picture above), and I realized that some herbicide spraying had been done recently. Then a large airboat came around the corner at a high speed. When he saw me, he was courteous enough to slow down. The boat was adorned with a Logo of a private aquatic plant spraying company. He was probably contracted with the Florida Fish and Wildlife Conservation Commission (FWC) or the St. Johns River Water Management District (SJRWMD) or perhaps some other agency. When he was well beyond my kayak, he continued his spraying. I do not know exactly what he was targeting—perhaps it was water lettuce, or the exotic grasses which grew along the shoreline.

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If you have ever been on a waterway just after it has been sprayed with herbicide, you know how disturbing it can be. To me it is similar to standing among dead trees stacked up in the middle of a forest or woodland which has been cleared for a road or for a new development. There is something ominous and foreboding about being surrounded by nature dying—even when the dying is supposedly limited to invasive exotic plants. If you believe herbicides are not toxic, or are just selectively toxic, just follow in the wake of one of these spray boats for a while.

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But these are thoughts of a native Floridian longing for the old days, not a pragmatist. And I know how important it is to remain pragmatic. While toxicity of herbicides is a concern, and we know some herbicides are more toxic than others, there is some validity to the argument that considerable  testing has been done on various herbicides, and that it can be argued that in some cases the use of herbicides can prevent or at least attenuate ecological disruption which could be associated with unrestrained growth of invasive aquatic plants.

But I would argue that when an aquatic plant management plan is oriented solely around killing these plants, the plan represents an attack on the consequences, while ignoring the cause. This is analogous to restricting our blame for lung cancer to the actual cancer cells (the consequence), while ignoring the significant role of cigarette smoking (the cause). The aquatic plants are the consequence of excessive nutrients. Excessive nutrient loading is the cause.

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Note that in 68F-20.0015(2) of the Florida Administrative Code (F.A.C) Aquatic Plant Management is defined as:

 

 “an activity designed to control the growth of aquatic plants so as to protect human health, safety and recreation and, to the greatest degree practicable, to prevent injury to non-target plants, animal life, and property.”

 

There is no mention of herbicides in this definition, and there certainly is no exclusion for efforts related to reducing nutrients in Florida’s waters. 

 

FWC and others involved with Aquatic Plant Management may suggest nutrient reduction is not their responsibility or the responsibility of their research partners at the University of Florida’s Institute of Food and Agricultural Sciences (IFAS) Center for Aquatic and Invasive Plants (CAIP), but rather is the charge of the Florida Department of Environmental Protection (FDEP) and EPA through the Total Maximum Daily Load (TMDL) program and the attendant implementation plans called Basin Management Action Plans (BMAPs).

 

The legislative directive to FWC regarding management of invasive aquatic plants, however, does not offer any relief from this responsibility:

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 “direct the control, eradication, and regulation of noxious aquatic weeds and direct the research and planning related to these activities . . . so as to protect human health, safety, and recreation and, to the extent possible, prevent injury to plant and animal life and property.”[10]

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This seems to indicate nutrient reduction activities would and should be included.  Cultivation of aquatic plants—including invasive aquatic plants—is clearly an effective means of reducing nutrients through removal and recovery of nutrients within plant biomass, and hence an effective way to “control……aquatic weeds.” Such cultivation would challenge the cause and thereby reduce the magnitude of the consequences.

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Perhaps it does not make sense to you to promote the cultivation of the very agent we are trying to “eradicate.” But actually, such a strategy is quite common in the wastewater treatment industry. Anyone who has ever worked on the design or operation of a domestic wastewater plant understands that the organisms used to remove oxygen-demanding pollutants within a treatment facility are the same organisms that in open surface waters would cause severe oxygen depletion should untreated, raw sewage be discharged. Management of these oxygen-depriving organisms within the receiving surface waters has not been by application of biocidal chemicals, but rather by using these same organisms within engineered facilities to remove the “food” within the final effluent prior to discharge. The strategy therefore is to eliminate the cause, not just attack the consequences. There is a direct parallel here regarding aquatic plant management. Why not use aquatic plants within a controlled cultivation facility to eliminate the cause of explosive aquatic plant growth in our surface waters—that cause being excessive nutrients? Such facilities would over time allow significant reduction if not elimination of the use of herbicides. This appears to be a reasonable strategy for moderation, by a two-pronged resolution--one targeting the consequences, the other targeting the cause.

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There are two facts that confirm that herbicide spraying that targets only the consequences, is a short term band-aid and not a long-term fix. The first of these facts is that targeted plant species are building resistance to certain herbicides, and it can be expected that this will continue. This means we will always be chasing new chemicals and combinations of chemicals, or using higher doses. Ultimately this becomes an Ouroboros—a snake eating its own tail. Such a situation may be attractive to chemical manufacturers, researchers and applicators, but not so good for our waterways' health or ours.

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The second fact is that herbicide spraying as noted does nothing to reduce nutrients within the water—in fact with each spraying the dead plants release their nutrients back to the water column, and these nutrients then help stimulate the growth of a new batch of aquatic plants to spray. The aquatic herbicide industry then is a self-perpetuating industry. It creates its own demand by assuring the plants continue to grow back.

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So now we must reluctantly enter the realm of politics. An objective party reviewing this situation would recognize that the most effective long-term approach to controlling aquatic plant growth is to reduce nutrients within the water. They would also realize that one potentially effective way to remove nutrients is to rely upon plant uptake and periodic harvesting through Managed Aquatic Plant Systems (MAPS). The Chinese are doing this on a large scale within targeted waterbodies. My experiences suggest to me that land-based kidney type systems would more effectively fit the U.S. culture, labor base, and economy. 

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So, to restate the strategy suggested earlier, perhaps the most viable long-term approach to aquatic plant management is to remove and recover waterborne nutrients through technologies such as MAPS, and combine these efforts with a reduction in nutrient imports associated with discharges, seepage and runoff. Once such a program is in place and has received approval by an at-large public committee, the use of acceptable herbicides can continue sparingly, recognizing that with falling nutrient levels, will come reduced rates of growth—see discussion around Figure 1—and a reduced demand for spraying. In a perfect world it would be hoped that nutrient concentrations could decline to levels that make it practical to use mechanical harvesting within the water body itself for management. As mentioned, the Chinese have come to recognize the effectiveness of this approach, and their successes in cultivating and recovering aquatic plants are being noticed around the world.

 

The arguments I have heard against the idea of using Managed Aquatic Plant Systems (MAPS) has been 1) it is very expensive and 2) there is no market for the crop. Of course, both of these barriers can be diminished significantly through a commitment to research and development, plus assistance to private interests who can refine this technology. And the transition from spraying to cultivation will over time facilitate a balance between jobs lost within the herbicide-spraying industry and new jobs created in the aquatic plant-cultivation industry.

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But there does persist a certain reluctance to take the Managed Aquatic Plant Systems (MAPS) approach seriously. Some of this undoubtedly comes from the human impulse to protect established cultures—in this case a culture oriented around herbicide application. I suggest this culture exists within the managing agencies such as the Florida Fish and Wildlife Conservation Commission (FWC); research entities such as the Center for Aquatic and Invasive Plants (CAIP) which is part of the University of Florida’s Institute of Food and Agricultural Services (IFAS); the herbicide application industry; and the various chemical manufacturers.

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Of course, it is likely each of these groups would offer some denial to this suggestion, for I believe it is human nature that encourages the development of such cultures.  Take for example the advocacy group for managing aquatic plants, The Florida Aquatic Plant Management Society (FAPMS). Their mission statement includes the following language:

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“To encourage and assist in:

1. Gathering and making available to supervisory and field personnel the most advanced information in all methods of aquatic plant management.

2. Research and development of herbicides to control aquatic plant.

3. Research and development of mechanical control of aquatic plants.

4. Research and development of biological control of aquatic plants.

5. Research and development of any other method or combination of methods that are potentially practical for field use.”

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But in looking at the agenda for their 2018 conference, I found there were 15 papers which were specifically related to herbicides and herbicide application, while only 1 paper on biological control, 2 papers on nutrient control and no papers on mechanical harvesting or aquatic plant cultivation methods such as MAPS.

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As another example, consider this statement by FWC regarding its Invasive Plant Management Section: 

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“Invasive plants degrade and diminish Florida's conservation lands and waterways.  Some invasive aquatic plants pose a significant threat to human welfare by impeding flood control and affecting recreational use of waterways and its associated surrounding economy.  The Invasive Plant Management Section funds scientific research projects at Florida's universities to improve the state's invasive plant management programs by finding more cost-efficient control techniques and also insuring these control methods are effective, safe, and environmentally compatible.  In addition, invasive plants can develop resistant to herbicides over time and new herbicides and/or herbicide combinations must be found through research in order to maintain good control.  Long term management solutions, like biological control research, can offer a permanent solution and can lower the need for herbicide use.”

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Notice no mention of cultivation, mechanical harvesting or nutrient control—again ignoring the cause. Then there is the statement from the University of Florida Institute of Food and Agricultural Sciences (IFAS) Center for Aquatic and Invasive Plants[11] (CAIP):

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“Invasive aquatic plants harm Florida’s natural environment and lead to a loss of biodiversity. They usually cannot be completely eradicated and will grow back quickly if not managed. The Florida Legislature designated the Florida Fish and Wildlife Conservation Commission (FWC) as the lead agency to “direct the control, eradication, and regulation of noxious aquatic weeds and direct the research and planning related to these activities . . . so as to protect human health, safety, and recreation and, to the extent possible, prevent injury to plant and animal life and property.” FWC currently controls about 12 of the most problematic aquatic invasive plants. In Florida, hydrilla and water hyacinth are two of the worst aquatic weeds, requiring constant attention and management.”

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Note how this statement emphasizes the negative aspects of these invasive aquatic plants. You might think I am being overly critical, but that is not my intent. Instead my hope is to encourage an adjustment to the culture such that efforts may be more effectively directed toward long-term solutions. For example, let me take a stab at rewording the IFAS statement (my add-ins are in red):

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“Expansive growths of Invasive aquatic plants have the potential to harm Florida’s natural environment and lead to a loss of biodiversity. This overgrowth is largely attributable to excessive nutrient loading within many of Florida’s surface and groundwaters, combined in many cases with the introduction of exotic species which compete successfully with native species. However, some invasive species, such as cattails can be native. The Florida Legislature designated the Florida Fish and Wildlife Conservation Commission (FWC) as the lead agency to “direct the control, eradication, and regulation of noxious aquatic weeds and direct the research and planning related to these activities . . . so as to protect human health, safety, and recreation and, to the extent possible, prevent injury to plant and animal life and property.” To meet this legislative responsibility the CAIP will partner with FWC and other involved agencies to implement a three- pronged approach for short and long-term management:

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1. Actively support aggressive research and development and eventual implementation of methods to reduce nutrient levels within Florida waters and watersheds, as high nutrient levels, more than any other factor, stimulate excessive growth of invasive plants. Such research and development should emphasize the benefits associated with the actual removal and recovery of nutrients, which includes, but not limited to, consideration of technologies involving purposefully controlled cultivation of select aquatic plants, some of which may also be considered invasive.

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2. Continue research, development and implementation of biological controls which target the selected invasive plant without deleterious ecological impact.

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3. Continue the herbicide application program as needed to manage excessive growth of invasive plants, while ensuring minimal impact upon the ecological stability of the targeted aquatic system, with any herbicide application program to gain approval by an effective at-large public oversight committee."

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In summary this revision includes recognition that what appear to be insurmountable problems can evolve into meaningful opportunities. In closing I would hope that FWC, CAIP and the other involved groups look past what may seem an assault on their purpose and existing programs and recognize an opportunity to establish a new, more expansive and helpful paradigm. With a commitment to such an adjustment, coordinated efforts will be necessary to identify funding needs and sources. It is time to move out of the box, take a deep breath, and work together for a better Florida!  

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[1] In fact, the Mayans in what is now Central America, apparently used this understanding over 1,500 years ago in replenishing soils with composted aquatic plants grown in highly nutritive wastewaters.

[2] Musil C.F. and C.M. Breen (1977) The application of growth kinetics to the control of Eichhornia crassipes (Mart) solms. Through nutrient removal by mechanical harvesting Hydrobiologia April 1977, Volume 53, Issue 2, pp 165–171

[3] This idea has been floating around for more than forty years and some investigations were conducted in Florida during that time, but never fully implemented. The Chinese are now successfully doing this on a large scale 

[4] Lineweaver, H. and Burke, D (1934) "The Determination of Enzyme Dissociation Constants" J. Am.Chem. Soc Vol 6, p 658

[5] Brezonik, P.L. (1993) Chemical Kinetics and Process Dynamics in Aquatic Systems Lewis Publishers, Boca Raton, Fl  ISBN 0-87371-431-8

[6] Stewart, E.A., D.L. Haselow, and N.M. Wyse (1984) "A Practical Model for Water Hyacinth Based Wastewater Management, Design and Operation" Water Ruse Symposium III, San Diego Califonia, USA

[7] Wolverton, B.C. and P.C. McDonald (1978) "Upgrading Facultative Stabilization Ponds with Vascular Aquatic Plans" NASA NSTL Station, Bay St. Louis Mississippi ERL Report 172 

[8] Bagnall, L.O. (1976) "Intermediate Technology Screw Presses for Dewatering Aquatic Plants" Instiute of Food and Agricultural Sciences, University of Florida, Gainesville, Fl.  USA

[9] In reality at 10 ppb total phosphorus we would expect water hyacinths to barely survive, much less grow to any extent.

[10] Chapter 369 F.S Conservation Part 1 Aquatic Plant Control (ss.369.20-369.255) 39.20 FS: Florida Aquatic Weed Control Act

[11] http://plants.ifas.ufl.edu/wp-content/uploads/files/mng/Why_We_Manage_Aquatic_Invasive_Plants.pdf

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