OKEECHOBEE — Low water levels in Lake Okeechobee combined with the summer heat set the stage for cyanobacteria (blue green algae) blooms in the Big O this summer. The lake is still recovering from the massive inflow of nutrients in 2017 from Hurricane Irma.
Over the past week, the algal bloom on Lake Okeechobee at the Port Mayaca Lock lessened in toxicity while a bloom in the inlet at Canal Point had high levels of microcystin.
The blue-green algal bloom observed within the wing walls of the Port Mayaca Lock on June 26, which had microcystin levels of 29 micrograms per liter, appeared to have lessened by July 2 when FDEP took water samples in the same area. The July 2 samples had microcystin levels of 3 micrograms per liter.
While the toxin levels in the windblown cyanobacterial bloom in the wing walls of the Port Mayaca locks lessened, toxin levels rose in a cyanobacterial bloom in the inlet canal to a water control structure at Canal Point.
The Florida Department of Environmental Protection June 26 report on a blue-green algal bloom in the Canal Point water control structure noted a heavy odor of bird excrement.
Bird droppings have been connected to the nutrient load elsewhere on the lake in the past. According to Dr. Paul Gray of Audubon Florida, bird droppings have been a recurring problem at the Pahokee marina over the years. Dr. Gray said at the Pahokee marina this is more common in the winter. He said there are usually not a lot of birds around the Canal Point area this time of year.
Cyanobacteria can move up and down in the water column, by inflating or deflating gas vesicles, but otherwise the movement of cyanobacteria is by wind or currents in the water. Wind-blown cyanobacterial blooms that are pushed into closed water control structures are trapped there. If there is a nutrient loading source, the cyanobacteria continues to reproduce, increasing its density in the water column. Not all cyanobateria are capable of producing toxins. Scientists are studying the factors that cause cyanobacteria to produce toxins, but anecdotal evidence indicates that when a cyanobacterial bloom capable of producing toxins is trapped in an enclosed space in hot weather and continues to be fed with phosphorus and nitrogen, it becomes more likely the toxin levels will increase.
A water sample taken from a blue green algal bloom in the inlet canal to water control structure S-352 near Canal Point on June 26 had microcystin level of 58.5 micrograms per liter. The EPA considers levels above 8 micrograms per liter as unsafe for human recreational contact. (The World Health Organization uses 10 micrograms per liter as the recreational contact level for microcystin.) The dominant taxon in the bloom was Microcystis aeruginosa. The bloom covered an area approximately 200 yards by 25 yards.
A sample taken in the same area at the Canal Point structure on July 1 had microcystin level of 63.6 micrograms per liter. A July 2 sample taken downstream of the water control structure in Palm Beach County had no toxins. Due to the low lake level, there has been no flow through the S-352 structure in recent weeks.
FDEP continues to monitor reports of algal blooms statewide.
An algal bloom near the LaBelle bridge in Hendry County on July 1 was mixed algae with no dominant species. No microcystin was detected.
A sample taken July 2 near the Port Mayaca lock on Lake Okeechobee had a microcystin level of 3 micrograms per liter. The dominant taxon was Microcystis aeruginosa.
On Friday, Lake Okeechobee was 11.31 feet above sea level, slightly up from the 11.26 feet level of the previous week. No water from the lake has flowed east to the St. Lucie Canal since March 30. Lake water is only released to Caloosahatchee River at Moore Haven if local basin runoff is not sufficient to meet the 450 cubic feet per second (cfs) minimum flow level to prevent saltwater intrusion in the river. In the past week, flow at the Moore Haven lock averaged only 59 cfs. Many days there was no flow from the lake. Flow at the Franklin Lock on the Caloosahatchee River averaged 1,676 cfs, for the week. which means an average of 1,617 cfs measured at the Franklin Lock was local basin runoff.
National Oceanic and Atmospheric Administration satellite images also show a high concentration of cyanobacteria near the northeast shore of the Florida Power and Light reservoir in Martin County. FDEP has not sampled that body of water.