SFWMD and FDEP officials are keeping a close watch on Lake O as conditions are ripe for algae...
South Florida Water Management District (SFWMD) and Florida Department of Environmental Protection (FDEP) officials are keeping a close watch on Lake Okeechobee as conditions are ripe for harmful algae blooms (HABs).
Cyanobacteria, commonly called blue-green algae, are part of the natural ecosystem of all lakes, streams and rivers. These microscopic organisms are believed to be the oldest life forms on the planet. According to the U.S. Geological Survey, 28 species of cyanobacteria have been documented in the Lake Okeechobee Waterway, which includes the Caloosahatchee River, Lake Okeechobee, the St. Lucie Canal and the St. Lucie River.
Most of the time the cyanobacteria are invisible to the human eye, but under certain conditions they can reproduce rapidly into a visible “bloom.” About 25% of the cyanobacteria are capable of producing toxins. But even those capable of producing toxins do not always do so. Algal blooms are not necessarily harmful. Hot weather, lack of water movement and available nutrients in the water (phosphorus and nitrogen) make conditions ripe for HABs.
Some species of blue-green algae are “nitrogen-fixers” and can use nitrogen from the air. Others, like the Microcystis aeruginosa commonly found in Lake O, cannot “fix” nitrogen and can only thrive if there is nitrogen in the water.
In 2022, runoff from Hurricane Ian dumped more than one million acre feet of water into Lake O, causing the lake level to rapidly rise, and bringing with it unknown levels of phosphorus and nitrogen. These nutrients can come from fertilizer in runoff and from legacy nutrient load. Nitrogen in runoff also comes from organisms in the soil that also “fix” nitrogen.
Before flood control, nature cleaned the water by slowly sheetflowing it over a wide floodplain. After Hurricane Ian, runoff from Orlando south was pumped down the Kissimmee Chain of Lake as rapidly as possible into the river and into Lake O to relieve flooding in urban areas.
FDEP monitors and manages blue-green algal blooms all over Florida. In addition, the SFWMD monitors and manages blue-green algal blooms in the district.
One part of managing the blue-green algae in the lake is regular water sampling to identify problem areas before they intensify. During the hotter months of the year, SFWMD samples water at 32 sites on the Big O twice a month. SFWMD and/or FDEP also samples any areas where visible blooms are reported. The week of May 15-17, SFWMD collected 32 routine samples and three algal bloom response samples.
Laboratory tests are required to determine which species of algae and/or cyanobacteria are present and if toxins are present. Often a “bloom” is a mixture of several species of algae and cyanobacteria.
The Environmental Protection Agency (EPA) considers microcystin levels below 1.0 parts per billion (ppb) to be safe for drinking water, and levels below 8.0 ppb to be safe for human recreational contact. At a meeting of the Florida Blue-Green Algae Task Force, officials explained “human recreational contact” includes swimming, and that levels are based on the safe level for small children, who they assume may swallow some water while swimming.
Of the 35 sites sampled, eight sites had trace levels of toxins (lower than the level considered safe for drinking water by the EPA), three sites had low levels of microcystin toxins (above the level for drinking water but below the level considered safe for human recreational contact); one site had toxin levels above the level for human recreational contact; the rest had no toxins detected.
• The C44 canal (aka St. Lucie Canal) had no dominant algal for samples taken at the Port Mayaca Lock (canal side) or at Port Mayaca Post (lakeside).
• The C43 canal (Caloosahatchee river) upstream of the Julian Keen Jr. Lock at Moore Haven sample was dominated by Microcystis aeruginosa and had no cyanotoxins detected.
• The S-252 spillway at Canal Point samples samples had no dominant algal taxon.
• C51 Canal (in Palm Beach County) upstream samples had no dominant algal taxon and no cyanotoxins detected.
The following Lake Okeechobee stations were dominated by Microcystis aeruginosa and had toxins detected. Toxin results follow each station name:
• L004 (trace level, 0.56 ppb);
• POLESOUT (1.0 ppb);
• POLESOUT3 (trace level, 0.49 ppb);
• KBARSE (trace level, 0.39 ppb);
The following Lake Okeechobee stations were dominated by Microcystis aeruginosa but had no cyanotoxins detected: L008, L005, POLESOUT2, POLESOUT1, NES135, NCENTER, PELBAY3, L006 and PALMOUT1.
The following Lake Okeechobee stations had no dominant algal taxon or cyanotoxins detected: KISSR0.0, LZ2, NES191, EASTSHORE, POLE3S and LZ25A.