Heavy rainfall in May and June followed by hot summer weather has led to increased reports of algal blooms and cyanobacteria blooms in South Florida.
Cyanobacteria, commonly referred to as “blue-green algae” is not actually algae.
A combination of hot weather, low salinity, nitrogen and phosphorus can cause algae and cyanobacteria to grow rapidly; this is called a “bloom.” Laboratory tests are required to determine what types of algae or cyanobacteria are in a “bloom.”
Some — not all — species of cyanobacteria produce toxins under certain conditions. Species that can produce toxins do not always do so.
The National Oceanic and Atmospheric Administration is monitoring what is believed to be a massive cyanobacteria bloom on Lake Okeechobee.
According to oceanographer Michelle Tomlinson of the NOAA National Ocean Service, they have been monitoring satellite photos of the lake since the start of June.
Ms. Tomlinson shared the following information about the images:
• A series of satellite images acquired on June 12, 20, 21, and 24 show the progression of a cyanobacterial bloom in Lake Okeechobee.
• On June 12, about 3 percent of lake area was covered by cyanobacteria blooms. Most of the blooms appeared along about a mile off the eastern shore.
• On the June 20 image, the bloom was observed to be covering about 49 percent of the lake surface area, mostly in the southwestern quadrant of the lake with some bloom accumulation along the northwestern shore.
• There was a decrease in bloom areal extent on June 21 of about 22 percent, where the bloom was observed along the eastern part of the lake. The decrease was likely due to wind mixing cyanobacteria cells down into the water column and not the disappearance of the bloom. These cells float back to the surface when winds subside.
• The latest image from June 24 shows the maximum cyanobacterial bloom extent observed in the month of June so far.
• The bloom was observed to be covering almost the entire lake area, excluding a narrow stretch along and about 6 miles off the eastern shoreline. Pronounced bloom accumulation was observed along the eastern shoreline.
“The algorithm we developed for the imagery is showing cyanobacteria blooms,” Ms. Tomlinson explained. “So it is separating out the cyanobacteria from any other background algae in the lake. There may be some non-harmful phytoplankton mixed in there, but what you are seeing is the concentration of the cyanobacteria.”
According to Dee Ann Miller of the Florida Department of Health: “Some — not all — blue-green algae can produce toxins that can contribute to environmental problems and affect public health. Little is known about exactly what environmental conditions trigger toxin production. Over time, these toxins are diluted and eventually break down and disappear. Persistent blooms are routinely monitored and retested. Because you cannot tell if algae is producing toxins by looking at it, the Florida Department of Environmental Protection (DEP) coordinates with the water management districts and the Florida Fish and Wildlife Conservation Commission to routinely sample observed and reported algal blooms and test for algal identification and toxin levels.”
Results posted by FDEP as of June 26 found no toxins in the samples collected in Lake Okeechobee since June 6. Earlier this month, very low levels of toxins of less than 1 microgram per liter were reported in samples from small blooms just off Lake Okeechobee’s east shore. The World Health Organization considers levels under 10 micrograms per liter as safe for recreational contact.
Samples were collected from various areas around the lake on Monday. Testing takes about four days.
NOAA is also tracking algae blooms in other areas of the country, such as Lake Erie and the Gulf of Maine.
On June 22, the U.S. Army Corps of Engineers changed the lake release schedule so that releases are measured at the Franklin Lock and limited the flow to 3,000 cubic feet per second (cfs). That’s about 1.6 billion gallons per day. Most of the water flowing through that lock is now from local runoff, not Lake Okeechobee.
For example, on June 25, the local basin runoff made up 2,028 cfs — more than two-thirds of the flow going through the Franklin Lock.
On June 25, releases at the Moore Haven Lock were 1504 cfs, so the flow to the Caloosahatchee estuary that day was about half lake water, half local basin runoff.
To the east, flow into the C-44 Canal from Lake Okeechobee has been reduced as well. That flow is measured at the St. Lucie Lock, so it includes water from the lake which enters the canal at Port Mayaca, as well as basin runoff that flows into the C-44 Canal between Port Mayaca and the St. Lucie Lock. In addition, the corps is pulsing the flows to allow the tides to flush out the estuary. On June 25, flow to the St. Lucie from the lake was just 195 cfs. Flow going through the St. Lucie Lock was 1,245 cfs. On June 26, flow from the lake at the Port Mayaca lock was 1,754 cfs.
On June 18, an algal bloom was reported on the Calooshatchee River near the LaBelle bridge. According to the FDEP tests, the bloom was mixed algae (not cyanobacteria) with no dominant species in the sample. No toxins were detected.
The most recent sample of algae near the St. Lucie Lock on Jume 21 found the dominant species was microcystin aeruginosa (a form of cyanobacteria). No toxins were detected. A sample taken June 19 at Port Mayaca found the same type of cyanobacteria. No toxins were detected.
A number of algal blooms were reported on Lake Okeechobee and connecting waterways on June 25. It takes four days to get test results, so the type of algae or cyanobacteria is not yet known.
FDEP investigated an algal bloom June 25 at the Ortona Lock. Dense mats of algae were observed at the surface along the canal bank. Algae was visible across the entire canal.
FDEP also inivestigated an algal bloom June 25 at the Alva Bridge. They found some surface alage which was sampled. They also collected samples at the Franklin Locks and the 41 bridge.
NOTE: Algal blooms and cyanobaceterial blooms look alike; it takes a microscope to the tell the difference. Cyanobacteria are prokaryotic organisms (a microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles) where as green algae are eukaryotic organisms (an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus.)
According to the Environmental Proection Agency, both algae and cyanobacteria occur naturally in freshwater worldwide. There are thousands of species of algae and thousands of species of cyanobacteria.