Chapter 5: Toxic Cyanobacteria in Florida Waters 

John Burns 

Florida Lake Management Society, 506 Emmett Street, Palatka, Florida 

32177 

Cyanobacteria represent a common component of algal assemblages in 

Florida’s lakes, springs, estuaries, and other marine environments. The 

frequency of cyanobacterial bloom reports has recently become more 

common and algal toxin data are just beginning to be collected with the 

advent of monitoring efforts and the availability of laboratories in the state 

capable of conducting algal toxin analyses. 

Given Florida’s growing population, subtropical environment, and the 

eutrophic nature of its lakes, rivers, and estuaries, it is not surprising that 

cyanobacteria are a common feature of aquatic ecosystems. However, 

cyanobacterial blooms may have always been common in some regions 

that include water bodies influenced by underlying phosphate deposits. 

Phosphate deposits cover much of peninsular Florida and are mined 

throughout the west–central part of the state (FIPR 2006; FDEP 2006). 

Although there is little doubt that the phenomenon of cyanobacterial 

blooms predates human development in Florida, the recent acceleration in 

population growth and associated changes to surrounding landscapes has 

contributed to the increased frequency, duration, and intensity of cyanobacterial blooms and precipitated public concern over their possible harmful effects to aquatic ecosystems and human health. Toxic cyanobacterial 

blooms in Florida waters represent a major threat to water quality, ecosystem stability, surface drinking water supplies, and public health. Many of 

Florida’s largest and most important lakes, rivers, and estuaries are increasingly impacted by toxic cyanobacterial blooms, including the St. 

Johns River (SJRWMD 2001), Lake Okeechobee (Havens et al. 1996), St. 

Lucie River (FFWCC 2005), Caloosahatchee River (Gilbert et al. 2006), 

and the Harris Chain of Lakes (LCWA, personal communication). Cyanobacteria, such as Lyngbya, are also common in many of Florida’s springs 
128 J. Burns 

and along coastal reef tracts where blooms form extensive mats and blanket corals and submersed aquatic vegetation. Shifts in phytoplankton composition to potentially toxic cyanobacteria taxa have also occurred in some 

eutrophic Florida lakes (Chapman and Schelske 1997). Historically, atopic 

sensitivity to cyanobacteria has been reported following exposure to algae 

in lakes. For example, Heise (1949) found blue–green algae responsible 

for seasonal rhinitis following exposure to algae while swimming in lakes. 

Human sensitivity to cyanobacteria may be related to a hereditary predisposition toward developing certain hypersensitivity reactions when exposed to specific antigens. 

There is a growing need in Florida and the other areas of the United 

States to define the specific relationships among freshwater cyanobacterial 

blooms, the production of secondary blooms in estuaries and marine 

coastal systems, and potential ecological and human health consequences 

associated with prolonged toxic bloom events. Moreover, because Florida 

lacks sufficient research and biomonitoring programs for toxic cyanobacteria, and little coordination exists between surface water managers and public health officials, relationships between toxic cyanobacteria and their environmental consequences remain largely in the realm of incidental 

observation and speculation. 

Historically, reports of cyanobacterial blooms in Florida are often associated with fish kill events in freshwater and estuarine systems. These reports often lacked specific algal identification information and toxin data 

was not collected. The earliest known record of algal toxins in Florida was 

reported following the death of cattle near Lake Okeechobee (Carmichael 

1992). Toxic cyanobacterial blooms in Florida were first recorded by 

Wayne Carmichael in Lake Okeechobee (1987, 1989) and Lake Istokpoga 

(1988). Dead cattle, signs of poisoning in laboratory mice, and contact irritation were found associated with Anabaena and Microcystis blooms. 

The toxin microcystin and an unidentified neurotoxin were attributed to the 

toxic effects found in Florida lake samples. Although toxic cyanobacterial 

blooms had become a major concern throughout the world, and the World 

Health Organization had set provisional guidelines for the consumption of 

microcystin– LR (WHO 1998), little information on toxic cyanobacteria in 

Florida waters had been published since those first toxic events identified 

in 1992.

No Florida survey of cyanobacterial blooms or cyanobacterial toxins 

had been conducted until the advent of the creation of the Florida Harmful 

Bloom Task Force in 1999. The Florida Legislature created the Harmful 

Algal Bloom Task Force in Chapter 370 F. S. “The Harmful–Algal–Bloom 

Task Force shall: (a) Review the status and adequacy of information for 

monitoring physical, chemical, biological, economic, and public health 
Chapter 5: Toxic Cyanobacteria in Florida Waters 129 

factors affecting harmful algal blooms in Florida; (b) Develop research and 

monitoring priorities for harmful algal blooms in Florida, including detection, prediction, mitigation, and control; (c) Develop recommendations that 

can be implemented by state and local governments to develop a response 

plan and to predict mitigate, and control the effects of harmful algal 

blooms; and (d) Make recommendations to the Florida Marine Research 

Institute by October 1, 1999, for research detection monitoring, prediction, 

mitigation, and control of harmful algal blooms in Florida.” In March 

1999, a technical advisory group to the Harmful Algal Bloom Task Force 

produced a report that identified known existing harmful algal species in 

the state and made recommendations for research and monitoring priorities 

(Steidinger et al. 1999). The report provided the following recommendations to the Task Force regarding toxic blue–green algae: 1) Determine distribution of toxic and non–toxic strains in Florida waters; 2) Develop epidemiological studies to determine what public health threats are involved; 

3)Develop economic impact studies to properly evaluate losses by locale 

or industry; and 4) Determine the roles of nutrient enrichment and managed freshwater flow in bloom development; 5) Investigate the applicability and efficacy of control and mitigation methods. 

Following the above recommendations, the Task Force funded an investigation of the occurrence and distribution of cyanobacteria and their toxins 

in 1999. The goals of the state–wide survey for the cyanobacteria survey 

included: 1) identification of toxic cyanobacteria throughout Florida; 2) 

identify and characterize level of cyanotoxins; 3) assist with the development of analytical capability for algal toxin analysis within the Florida Department of Health laboratory in Jacksonville, Florida; and evaluate the 

presence of cyanobacterial toxins at water treatment plants that utilize surface water resources. 

The FHABTF, Florida Marine Research Institute, and St. Johns River 

Water Management District initiated a collaborative study with the Florida 

Department of Health and Wright State University to identify potential 

cyanobacterial toxins in Florida’s lakes, rivers, reservoirs, and estuaries. 

Samples were collected and analyzed during 1999 and then extended to 

better understand the potential impacts of cyanobacterial toxins detected in 

waters currently utilized for drinking water or identified as a potential future drinking water source. 

Methods employed to identify alga taxa included microscopic examination and epifluorescence. Algal toxins were characterized and quantified 

by enzyme linked immunosorbant assay (ELISA), protein phosphatase inhibition assay (PPIA), HPLC–Fl, HPLC–UV, and LC/MS/MS. Mouse 

bioassays were used to characterize toxicity by intraperitoneal injection of 

freeze–dried sample extracts into ICR–Swiss male mice. 
13

With the assistance of numerous state and local agencies in 1999, a total 

of 167 samples were collected throughout Florida, eighty–eight of these 

samples, representing 75 individual water bodies, were found to contain 

cyanotoxins. Approximately 80% of the samples containing cyanotoxins 

were found to be lethal to mice following intraperitoneal injection. Most 

bloom forming cyanobacteria genera were distributed throughout the state, 

but water bodies such as Lake Okeechobee, Harris Chain of Lakes, Lower 

St. Johns River, Calooshatchee River, Lake Seminole, Lake George, Crescent Lake, Doctors Lake, and the St. Lucie River were water bodies that 

supported extensive cyanobacterial biomass. Seven genera of cyanobacteria were identified from water samples collected. Microcystis (43.1%), 

Cylindrospermopsis (39.5%), and Anabaena (28.7%) were observed most 

frequently and in greatest concentration. Planktothrix (13.8%), Aphanizomenon (7.2%), Coelosphaerium (3.6%) and Lyngbya (1.2%) were 

found less frequently, but at times accounted for a significant proportion of 

the planktonic and macroalgal species composition. Aphanizomenon and 

Anabaenopsis were also found consistently during the 2000 survey. 

Cyanobacterial blooms were common throughout the state, some of which 

form long lasting or continuous blooms in eutrophic and hypereutrophic 

systems. Many of the water bodies affected by cyanobacterial blooms 

were identified by water management agencies as areas of current concern 

or were being addressed by ongoing or proposed restoration efforts. 

Algal toxins identified from bloom material during the study included 

hepatotoxic microcystins, neurotoxic anatoxin–A, and the cytotoxic alkaloid cylindrospermopsin. Subsequent identification of lyngbyatoxin–A 

and debromoaplysiatoxin were found associated with Lyngbya blooms collected from Florida springs and coastal embayments. Microcystins were 

the most commonly found toxins in Florida waters, occurring in all 87 

samples analyzed during 1999. During the 2000 survey, microcystins were 

detected in pre– and post–treated drinking water. Finished water microcystin concentration ranged from below detection levels to 12.5 μg L-1. 

Microcystins are considered the most frequently found cyanobacterial toxins around the world. Over 60 structural variants of this cyclic peptide 

have been reported, causing considerable concern due to their high chemical stability, high water solubility, environmental persistence and exposure 

to humans in surface water bodies. The World Health Organization has set 

a provisional consumption limit of 1 μg L-1 for microcystin–LR (WHO 

1998). The mammalian toxicity of microcystin occurs by active transport 

across membrane boundaries and is mediated through binding to protein 

phosphatases (Runnegar et al. 1991; Falconer et al. 1992). Analysis of 

protein phosphatase inhibition activity, an index of microcystin bioactivity, 

was found to be positive in 44 (69%) of 64 Florida samples tested. There 

0 J. Burns 
Chapter 5: Toxic Cyanobacteria in Florida Waters 131

is limited evidence of tumor promotion (Sato et al. 1984; Falconer 1991, 

Nishiwaki–Matsushima et al. 1992, Wang and Zhu 1996) and clastogenic 

dose–related increases in chromosomal breakage by microcystin (Repavich 

et al. 1990), but no mutagenic evidence has been reported (Runnegar and 

Falconer 1982, Repavich et al. 1990). 

Anatoxin–a is a potent neurotoxic alkaloid that has been frequently implicated in animal and wildfowl poisonings (Ressom et al. 1994). It is 

considered a nicotinic agonist that binds to neuronal nicotinic acetylcholine receptors which leads to depolarization and a block of electrical transmission in the body (Soliakov et al. 1995). At sufficiently high doses (oral 

LD50 = >5,000 μg kg-1 body weight), it can lead to paralysis, asphyxiation, and death (Fitzgeorge et al. 1994, Carmichael 1997). Although alternative hypotheses exist to help explain alligator mortalities in Florida 

lakes, unexplained bird and alligator mortality events during cyanobacterial blooms may be due to exposure to neurotoxic compounds produced by 

species of Anabaena, Aphanizomenon, and Cylindrospermopsis. Anatoxin–a was found in three finished water samples and in tissues from Blue 

Tilapia and one White Pelican during surveys in 2000. Anatoxin–a was 

found in the gut and liver of a White Pelican and in Blue Tilapia (0.51 to 

43.3 μg g-1 ) and in finished drinking water (below detectable limits to 8.46 

μg L-1). 

All 1999 samples containing the organism Cylindrospermopsis were 

positive for the toxin cylindrospermopsin. Nine (9) finished drinking water samples collected during the 2000 survey were positive for cylindrospermopsin and ranged in concentration from 8.07 to 97.12 μg L-1. Identification of the algal toxin cylindrospermopsin during this study represented 

the first record of this hepatotoxic alkaloid in North America. This toxin 

primarily affects the liver, but extracts given orally or injected in mice also 

induce pathological damage to kidneys, spleen, thymus, and heart (Hawkins et al. 1985, 1997). Cylindrospermopsin is a potential important contaminant of drinking waters in Australia, Central Europe, South America, 

and the United States. The toxin was identified after 138 children and 10 

adults were poisoned following a Cylindrospermopsis bloom and copper 

sulfate applications in a water supply reservoir on Palm Island, Australia 

(Hawkins et al. 1985). Over 69% of the affected individuals required intravenous therapy for electrolyte imbalance, and the more severe cases for 

hypovolemic and acidotic shock (Byth 1980). The oral toxicity or lethal 

dose of cylindrospermopsin has been reported between 4.4 and 6.9 mg kg-1

mouse body weight with death occurring 2–3 days after treatment (Humpage and Falconer 2002). In experiments where cell free extract of Cylindrospermopsis was administered to mice in drinking water over 90 days, 

no pathological symptoms were recorded up to a maximum dose of 150 
13

mg kg-1 day-1 (Shaw et al. 2001). Humpage and Falconer (2002) suggest a 

Tolerable Daily Intake and Guideline Value for cylindrospermopsin in 

drinking water of 1 μg L-1based on an oral No Observed Adverse Effect 

Level of 30 μg kg-1 day-1 and a Lowest Observed Adverse Effect Level of 

60 μg kg-1 day-1. 

Lyngbyatoxin–a and debromoaplysiatoxin have been identified from 

Lyngbya samples collected from Florida springs and marine embayments, 

respectively (J. Burns, N. Osborne, and G. Shaw, unpublished data). The 

aplysiatoxins and lyngbyatoxins are considered dermatotoxic alkaloids, 

causing severe dermatitis among swimmers and other recreational users of 

water bodies that come into direct contact with the organism (Mynderse et 

al. 1977, Fujiki et al. 1982). Aplysiatoxins are lethal to mice at a minimum 

dose of 0.3 mg kg-1 (Moore 1977). Aplysiatoxins and lyngbyatoxins are 

also considered potent tumor promoters and protein kinase C activators 

(Fujiki et al. 1990). Osborne et al. (2001) reviewed the human and ecological effects of Lyngbya majuscula blooms and reported acute contact 

dermatitis in Hawaii, Japan, and Australia. One potential death due to exposure via ingestion of turtle meat containing lyngbyatoxin– a was reported by Yasumoto (2000). Severe dermatitis has also been reported in 

Florida following recreational activities in waters supporting Lyngbya

blooms in Florida’s springs (John Burns, Ian Stewart and G. Shaw, unpublished data). Lyngbya mats have been detected along coral reef tracts adjacent to the southeast coast of Florida near Dade and Broward counties. Although no toxins have been detected from the limited number of samples 

analyzed, thick mats of Lyngbya have smothered corals, causing severe 

damage to the reef. 

To date, toxic cyanobacterial blooms continue to occur throughout Florida and no state–wide monitoring program for cyanobacteria or cyanobacterial toxins exists. No Florida guidelines for recreational exposure to toxic 

cyanobacteria or cyanobacterial toxins in drinking water are available. 

However, several independent monitoring efforts for cyanobacteria and 

their toxins have been initiated and the Florida Harmful Algal Bloom Task 

Force has helped fund the following efforts, “Cyanobacteria Automated 

Detection Workshop”, “Cylindrospermopsis Culture for Production of Cylindrospermopsin”, and “Cyanobacteria Public Health Issues: Education 

and Epidemiologic Study Monitoring and response efforts have been initiated by the St. Johns River Water Management District (Lower St. Johns 

River Basin), South Florida Water Management District (Lake Okeechobee), Lake County Water Authority (Harris Chain of Lakes), Florida Lake 

Watch, and several water utilities in the state that utilize surface waters for 

2 J. Burns 
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Chapter 5: Toxic Cyanobacteria in Florida Waters 135 

The prevalence and toxicity of cyanobacteria should be considered when 

developing appropriate Total Maximum Daily Loads for impaired Florida 

waters that do not currently meet their designated use. It could also support further efforts to characterize potential ecological and human health 

risks due to toxic cyanobacterial blooms. Identification of algal toxins in 

finished drinking water and reports of severe skin irritation following contact with toxic cyanobacteria should be utilized for justification and implementation of increased monitoring of potentially toxic cyanobacterial 

blooms by surface water managers and water utilities. Epidemiological 

studies may also be required in Florida to assess potential human health 

risks due to algal toxin consumption at the tap and for those exposed to 

cyanotoxic blooms during recreational use of lakes, springs and rivers. 

Without adequate water treatment and coordinated state–wide monitoring efforts, it is anticipated that the likelihood for human exposure to 

cyanobacteria and their toxins will increase as Florida becomes more dependent upon surface waters to supply a growing population and an expanding urban environment. Coordination and communication between 

surface water managers and public health officials at the local level will be 

critical to the overall protection of the environment and public health during toxic cyanobacterial bloom events.

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Chapter 5: Toxic Cyanobacteria in Florida Waters 137