As the level of Lake Okeechobee continued to drop last week, area officials hoped the wet season rains will arrive on time.

On Monday, Lake Okeechobee was 10.83 feet above sea level, according to the U.S. Army Corps of Engineers.

Lake releases to the Caloosahatchee River were reduced from 800 cubic feet per second to 450 cfs. on Saturday. Freshwater flow to the Caloosahatchee is measured at the Franklin Lock, which is 43.4 miles from the Moore Haven Lock. Some of the flow measured at the Franklin Lock is local basin runoff.
While no lake water has been released to the St. Lucie Estuary since March 30, there has been some flow back and forth at the Port Mayaca Lock. Flow to the St. Lucie Estuary is measured at the St. Lucie Lock which is 23.9 miles from Port Mayaca.

When the lake is low, the corps allows local basin runoff that flows into the St. Lucie Canal to flow west, into Lake Okeechobee.

According to the U.S. Army Corps of Engineers, the practice of dealing with local basin runoff through Port Mayaca is common and has been going on since the beginning of the dry season. When the lake is below 14 feet, it is common operating procedure to have Port Mayaca open their lock chamber to allow an open pass for navigation and to equalize the canal with the lake, a corps spokesperson explained. When local basin runoff allows the water level in the canal to rise higher than the lake, there can be flow from the canal to the lake. All flow at Port Mayaca is gravity driven.

As temperatures rise, most of the water leaving the lake is evaporating into the air or percolating into the aquifer.

Boat ramps closed
The low lake level means all of the locks on the north shore of the lake have been closed to boat traffic. Lake access is available at boat ramps inside the Herbert Hoover Dike and on the Kissimmee River.

Boat ramps that provide access include: Clif Betts Jr. Lakeside Recreation Area (Lock 7), Okee-Tantie Recreation Area Airboat Ramp, Okee-Tantie Recreation Area Marina and Boat Ramp, C. Scott Driver Recreational Area, Indian Prairie Canal Public Boat Ramp at State Road 78, Bare Beach Boat Ramps, Harney Pond Canal – Margaret Van de Velde Park – Southern Canal Side Boat Ramp, Lakeport Boat Ramp and Old Sportsmans Village.

On the south shore, the S-310 lock at Clewiston in Hendry County remains open.

The hot weather also brings with it concerns about increased potential for algal blooms.

Blue-green algae
The National Oceanographic and Atmospheric Administration (NOAA) uses satellite imagery to postulate the potential for increases in cyanobacteria (commonly called blue green algae) in the lake. Rick Stumpf 0f NOAA explained that Sentinel-3a, part of the European Union’s Copernicus program, was built by the European Space Agency (ESA) and operated by EUMETSAT (EU Meteorological Satellite office). It was launched in 2016, data became available in 2017. A matching satellite Sentinel-3b was launched in April, and should start providing routine data in 2019.

The satellite looks at the amount of light in many wavelengths. To detect cyanobacteria we use several wavelengths of red and near-infrared light (this infrared detects brightness, not temperature). For water, only the light from the upper 1-3 feet is measured. Differences between these bands detect pigments that are characteristic to cyanobacteria.

Red means high concentration, followed by orange, yellow, green, then blue. Black is “not detectable,” concentrations too low to see or be a risk. Green and above have concentrations that the World Health Organization has found typically causes a risk to human health from direct exposure. Blue colors indicate some risk is possible. Areas with “green” colored concentrations (> 100,000 cells/mL) have potential for small patchy scums. Areas with “red” concentrations (1 million cells/mL) will have large scum areas.

He said the satellite imagery can show cyanobacteria present when those in a boat do not see it. The satellite can see details we cannot see, so can see high concentrations even when there is not a scum, he explained.

“From a boat, we can only see about 20 yards around, while the satellite pixel covers the area of a football stadium. If you look closely at the water from your boat you might see flecks of what looks like green sawdust in the water,” he explained.

The cyanobacteria in Lake Okeechobee tends to float up in early day, and sink in late day. If winds are light or calm, it will form a scum. As wind picks up it prevents scum formation, and strong winds can mix the bloom down into the water, so it is less visible.

The imagery cannot detect the species of cyanobacteria present. It cannot tell if there are any toxins present.

Year-round, the Florida Department of Environmental Protection investigates reports of algal blooms and takes samples where blooms are visible. Not all algal blooms are cyanobacteria. Of the dozen or so species of cyanobacteria commonly found in Lake Okeechobee, only a few are capable of producing toxins, and those capable of producing toxins do not always produce toxins. Laboratory tests determine the type of algae and/or blue-green algae present and toxin levels, if any. On May 28, a sample was taken at the Pahokee marina. Tests revealed mixed algae with no dominant species. No toxins were detected.

Since the start of the dry season, most tests on water from the lake found no toxins or very low levels of toxins. The highest toxin level found was in a sample taken May 22 northeast of Clewiston. The dominant species in the sample was Microcystis aeruginosa, a cyanobacteria common to the lake. Microcystim level was 2.08 micrograms per liter. The Environmental Protection Agency recently set the level safe for human recreational contact at levels below 8 micrograms per liter. The World Health Organization Standard is 10 micrograms per liter.

County coalition meets
Representatives from Okeechobee, Glades, Hendry, Palm Beach, Highlands, Lee, Martin, Oceola and St. Lucie counties will gather Friday, June 7, at the County Coalition for Responsible Management of Lake Okeechobee, the St. Lucie and Caloosahatchee Estuaries and the Indian River Lagoon meeting, at 9 a.m. in the Historic Okeechobee County Courthouse, 304 N.W. Second Street in Okeechobee. The agenda includes a report from the South Florida Water Management District and a report from the U.S. Army Corps of Engineers. The meeting can be watched live online at co.okeechobee.fl.us.