See an algal bloom? Don’t swim there

Posted 6/7/19

On May 24, the Environmental Protection Agency released new guidelines for contact with cyanotoxin levels, advising that levels above 8 micrograms per liter of microcystin are unsafe for human …

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See an algal bloom? Don’t swim there


On May 24, the Environmental Protection Agency released new guidelines for contact with cyanotoxin levels, advising that levels above 8 micrograms per liter of microcystin are unsafe for human recreational contact. This is a change from the World Health Organization recommendations which found levels under 10 micrograms per liter to be safe for recreational contact.

The news did not appear to concern those who enjoy spending their days on Lake Okeechobee.

First, the microcystin toxins in samples collected from areas where there is visible algae in the lake are well below the new standards. Even during the coastal communities’ “lost summers” when thick mats of blue green algae drove coastal residents from their waterways, the toxin levels in most samples from the lake were barely detectable, according to the Florida Department of Environmental Regulation algae tracking website. In the summer of 2008, when NOAA satellite imagery indicated that 90 percent of Lake Okeechobee contained cyanobacteria, the toxin levels in the lake water were low.

So far this year, the highest microcystin level found on the lake was 2.08 micrograms per liter in a sample from an algae bloom on the lake northeast of Clewiston on May 22, according to the FDEP Algal Bloom Monitoring website.

Second, and most importantly, most people don’t swim in Lake Okeechobee, due to a healthy respect for the alligators who make the Big O their home.

The Florida Department of Environmental Protection is reviewing the EPA’s new guidelines. If FDEP updates the state standards, it could mean more warning signs along coastal waterways.

Most lake area residents just follow the common sense advice provided in previous years by FDEP: If you can see an algal bloom, don’t swim in that water, don’t let your pets swim in the water and don’t let your pets drink the water.

FDEP continues to offer that advice: If a visible algal bloom is present, stay out of the water. You can’t tell if an algal bloom is producing toxins by looking at it. Better to err on the side of caution.

According to FDEP, most algae does not product toxins harmful to humans, and the species of blue green algae that are capable of producing toxins do not always produce toxins. Scientists are still trying to determine what factors or combination of factors cause blue green algae to sometimes produce toxins. Something about the coastal waterways apparently may cause the blue green algae to produce toxins at higher levels.
Many of the same precautions apply to both algae and alligators. Consider:

• Both algae and alligators are found year round in Lake Okeechobee, as well as waterways throughout the state. According to the Florida Wildlife Commission, there are an estimated 1.3 million alligators in Florida. They live in all 67 counties. According to the Florida Department of Environment Regulation, algae (and cyanobacteria which is called “blue-green” algae) can be found naturally in all freshwater and brackish water. There are thousands of types of algae and cyanobacteria. About a dozen types of blue-green have been documented in Lake Okeechobee by the University of Florida.

• Both algae and alligators are more noticeable during certain seasons. Alligators are more active during mating season. Algae is more likely to be visible in the summer when the heat and rainfall provide the right conditions for it to reproduce.

• Just because you don’t see algae or alligators doesn’t mean they are not there. Blue-green algae are microscopic. An algae bloom occurs when algae reproduce rapidly into a concentration that is visible. Blue-green algae can rise and fall in the water column, so it might not be visible on the water surface. According to, alligators often stay submerged for 20 to 30 minutes at a time, and under certain conditions can stay underwater much longer. Most of the time, this is not a problem. Alligator attacks on humans are rare. Most algae and cyanobacteria is not toxic. Even cyanobacteria that can produce toxins does not always do so.

• Both the algae and the alligators are part of the natural ecosystem. Algae and alligators were here before the humans arrived.

• Feeding algae or alligators can result in situations harmful to humans. When humans feed alligators, it causes them to connect humans with food and causes them to lose their natural aversion to people. Feeding the algae is also dangerous. High levels of phosphorus and nitrogen, along with hot weather, can result in high concentrations of algae in the water. Humans are responsible for increasing that nutrient load into the waterway, by using fertilizer on lawns, golf courses and farms and by creating drainage systems that move water faster instead of slowly filtering through marshes. Human action also increases the nutrient load from leaking septic tanks, sewage spills and landspreading of biosolid waste.
Under certain conditions, some blue-green algae can produce toxins harmful to humans.

• FWC advises people to stay out of the water in areas where alligators are seen. An alligator may react to splashing of a person swimming the same way it reacts to its normal prey. Florida Department of Health (FDOH) advises people stay out of the water if algae is visible. You can’t tell if an algae bloom is toxic just by looking at it. If toxins are present and you swim in the water, you might develop a rash. If you swallow water containing toxins, it could result in other health issues.

• FWC advises residents to keep pets out of the water if you see alligators. Alligators will treat a dog that is in or near the water as their prey. FDOH advises keeping pets out of the water if you see algae, as pets may swallow some of the water and become ill.

• Development of cities and subdivisions has resulted in increased hazards from both algae and alligators. Development results in more runoff and higher levels of phosphorus and nitrogen in the runoff, which feed algae blooms. Development displaces alligators (and other wildlife) causing more interactions with people.

• Algae and alligators are both affected by temperature changes. Hot weather is a factor in algae blooms. According to the FWC, alligators rely on an external source of heat to regulate their body temperature. They become dormant when their body temperature drops below 55 degrees Fahrenheit.

• Too much algae … or too many alligators … creates problems. The State of Florida tries to control both.