Algae blooms are common on Lake Okeechobee when the summer sun heats up the water. While algae is part of the natural ecosystem, some species of algae can produce toxins that may be harmful to humans. This year, the South Florida Water Management District, Florida Department of Environmental Protection and U.S. Army Corps of Engineers have teamed up to identify, test, target and treat harmful algal blooms before they turn into public health hazards.
Cyanobacteria, commonly called blue-green algae, are part of the natural ecosystem of the Lake Okeechobee Waterway, which includes the Caloosahatchee River, Lake Okeechobee, the C-44 canal (also called the St. Lucie Canal) and the St. Lucie River. Most cyanobacteria do not produce toxins. About a quarter of the 28 different species of cyanobacteria documented by the U.S. Geological Service are capable of producing toxins. Without laboratory tests, it’s impossible to know what species of cyanobacteria are present in a bloom. Tests are also needed to determine if toxins are present. Cyanobacteria capable of producing toxins do not always do so. According to information shared in meetings of the Florida Blue-Green Algae Task Force, scientists still don’t know exactly what causes cyanobacteria to produce toxins.
To protect public health, state and federal agencies have increased monitoring, sampling and testing in order to identify algal blooms and determine which ones have the potential to produce toxins, and treat harmful algal blooms before they become health hazards.
The National Oceanic and Atmospheric Administration (NOAA) satellite imagery is one tool scientists use to track blooms. However, the NOAA images do not depict actual blooms – these images show bloom “potential” based on the levels of chlorophyll in the water. The NOAA imagery from June 23 shows bloom potential in approximately 45% of the big lake. According to information shared at Blue-Green Algae Task Force meetings, other biological material in Lake Okeechobee could cause the NOAA images to give false readings. The NOAA image shows areas of low bloom potential in blue, moderate bloom potential in green and high bloom potential in red or orange. Fishermen often report finding no visible algae in areas the satellite images indicate heavy bloom potential.
During the summer, SFWMD and the Florida Department of Environmental Protection (FDEP) increase water sampling at designated sites. FDEP also visits sites of algae blooms reported by the public.
June 22 and 23, SFWMD staff performed bimonthly routine harmful algal bloom (HAB) monitoring on Lake Okeechobee. Eleven stations were dominated by Microcystis aeruginosa; five were dominated by Cylindrospermopsis raciborskii; two were co-dominated by either Microcystis aeruginosa and Cylindrospermopsis raciborskii or Cylindrospermopsis raciborskii and Dolichospermum circinale; and 10 had no dominant algal taxon. All the samples dominated by Cylindrospermopsis raciborskii were on the northern half of the lake.
Most of the samples detected no toxins. The World Health Organization considers toxin 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 (swimming).
Microcystin results are included in parentheses in parts per billion (ppb) following each station name:
• KISSRO.0 (non-detect);
• LZ2 (non-detect);
• NES191 (non-detect);
• L001 (non-detect);
• NES135 (trace, 0.42 ppb);
• NCENTER (non-detect);
• EASTSHORE (trace, 0.11 ppb);
Due to heavy rainfall in the basin since the start of the wet season, very little water has been released from Lake Okeechobee to the Caloosahatchee River for the past month. On June 22, U.S. Army Corps of Engineers conducted limited releases for a U.S. Geological Service sediment study. The target flow at the Franklin Lock is 1,000 cubic feet per second (cfs). When there is sufficient local basin runoff to meet that target, no lake water is released at Moore Haven. The Julian Keen Jr. Lock at Moore Haven is more than 40 miles from the Franklin Lock.
For the seven day period ending June 24, flow at the Franklin Lock averaged 1,736 cfs and flow at the Julian Keen Lock averaged 89 cfs.
Water samples taken from the river in the past week had no toxins.
• On June 20 and 21, So SFWMD staff collected samples upstream of the Julian Keen Lock and upstream of the Franklin Lock. The upstream sample from the Franklin Lock was dominated by Cylindrospermopsis raciborskii. No toxins were detected. The sample from upstream of the Franklin Lock had no dominant algal species and no toxins detected.
• A sample taken June 21 from the Caloosahatchee River near the Sebastian Canal found mixed algae with no dominant species. No toxins were detected.
• A sample taken June 21 from the Caloosahatchee River near Rosen Park found mixed algae with no dominant species. No toxins were detected.
• A sample taken on June 22 from the Caloosahatchee River near Palaco Grande Canal found mixed algae with no dominant species. No toxins were detected.
• A sample taken June 22 from the Caloosahatchee River near Plato Canal (near Cape Coral) had microcystis aeruginosa as the dominant species. Microcystis is capable of producing toxins, but no toxins were detected.
• A sample taken on June 22 from the Caloosahatchee River near the Bimini Canal found mixed algae with no dominant species. No toxins were detected.
• A sample taken on June 22 from the Caloosahatchee River at the Cape Coral Yacht Club Basin found mixed algae with no dominant species. No toxins were detected.