The good news: The surface of Lake Okeechobee is NOT covered in blue-green algae, toxic or otherwise.
The bad news: According to the National Oceanic and Atmospheric Administration (NOAA), there is a large concentration of cyanobacteria (sometimes called “blue-green algae”) in the lake. According to the Florida Department of Environmental Protection, some of the samples taken from areas along the shore where winds pushed algae and cyanobacteria into clumps along the shoreline have shown low levels of toxins.
What happens next: According to the scientists who study algae worldwide, there is no way to tell, at this point, what will happen as the summer heat continues.
The NOAA image of the lake from Monday, July 2, shows varying concentrations of cyanobacteria in about 90 percent of Lake Okeechobee. The NOAA imagery does not indicate what kind of cyanobacteria is present. There are thousands of types of cyanobacteria, although only about a dozen have been documented in Lake Okeechobee.
Some — not all — of the types of cyanobacteria known to live in the lake can produce toxins under certain conditions. However, even cyanobacteria that can produce toxins does not always do so.
This widely publicized NOAA image confused some who saw it. Sen. Bill Nelson, who flew over the lake on July 5, said he was pleasantly surprised that he did not see a massive bloom on the surface of the lake.
“As I flew over the lake, I was glad to see there was not algae on the 80 percent of the lake I was led to believe,” he said.
Boaters who were out on the lake over the past week also reported they did not see algae.
Anglers continue to give the lake good reports for fishing this summer.
No algae was visible from the north shore at the Clif Betts Jr. Lakeside Recreation Area (aka Lock 7) last week. From the bridge at Port Mayaca, no algae was visible on the surface of the vast expanse of Lake Okeechobee. No algae could be seen near Torry Island, where Sen. Nelson and Congressman Alcee Hastings held a press conference on July 5.
An algal bloom was reported on the surface at the Pahokee marina. FDEP sampled a bloom at the Port Mayaca Lock on July 2. Dr. Edward Phlips, a professor with the University of Florida’s Department of Fisheries and Aquatic Sciences, said the casual observer may not even notice the bloom.
“Massive blooms don’t always start at the surface,” he explained. “It can be in the water column.”
Cyanobacteria have gas vesicles that act as buoyancy control devices. The vesicles can be expanded and filled with gas, causing the cyanobacteria to float on the surface, or deflated, which causes the cyanobacteria to descend into the water column. “Just because you don’t see it doesn’t mean there’s nothing going on,” he said. The NOAA image does not show what the human eye sees. It’s computer-generated imagery using data the satellite collects to locate concentrations of cyanobacteria in the water. Different colors on the imagery show areas of varying cyanobacteria concentration. The NOAA image does not show how many different types of cyanobacteria are present, or which types of cyanobacteria are present. They also do not show whether toxins are present.
Oceanographer Michelle Tomlinson of the NOAA National Ocean Service explained they have been monitoring satellite photos of the lake since the start of June. They do similar studies of other lakes in the United States. “The algorithm we developed for the imagery is showing cyanobacteria blooms,” she 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.” Oceanographer Rick Stumpf with the NOAA National Centers for Coastal Ocean Science, explained: “The satellite can see high concentrations of the bloom when it is not forming a dense scum, and scum is the only thing we easily see from an airplane.
“When winds are light or calm, the cyanobacteria that makes the algae bloom tends to float up in the day, and sinks late day and at night. Calm weather, in the early to mid-day usually leads to scum. When winds pickup they tend to mix the bloom through the water so that less of it is at the surface, so it is not so apparent.”
He explained that NOAA also uses different wavelengths of light, including red and near-infrared, that the satellite detects that can’t be seen with the human eye. Dee Ann Miller of the Florida Department of Health explained: “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 (FDEP) 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.” Some samples taken from the lake have shown no toxins. Others have shown low levels. The World Health Organization considers levels below 10 micrograms per liter to be safe for recreational contact. On June 18, algae from a dense film windblown against a water control structure in Palm Beach County had 1.4 micrograms per liter. On June 25, a sample taken at the Port Mayaca Locks had 2.2 micrograms per liter. That same day, a sample taken at the Moore Haven Lock had 3.3 micrograms per liter. On July 2, a sample taken from a surface bloom on the lake near Port Mayaca had 1.9 micrograms per liter of microcystin. Test results on samples collected by FDEP on July 5 are not yet available.
Dr. Karl Havens, director of Florida Sea Grant and a professor at the University of Florida, said that even in a small pond, toxin levels may vary from one area of a cyanobacterial bloom to another.
In a large ecosystem such as Lake Okeechobee, sometimes the cyanobacteria won’t produce toxins at all, he explained.