The latest sample of algae in Lake Okeechobee found the water safe for human contact, according to the Florida Department of Environmental Protection data.

A sample taken of a windblown algal bloom at the Port Mayaca Lock had microcystin levels of 1.08 micrograms per liter, according to FDEP. The new Environmental Protection Agency standard for safe for human contact is 8 micrograms per liter. The previous standard, set by the World Health Organization, was 10 micrograms per liter. The EPA does not currently regulate microcystins in drinking water, but in 2015, the EPA published a Health Advisory that recommended 1.6 micrograms per liter as a level not to be exceeded for school-age children and adults, and 0.3 micrograms per liter as a level not to be exceeded for pre-school age children, and based on exposure for 10 days.

• The NOAA satellite imagery from June 3 shows a blue-green algal bloom. The area in red is the highest concentration of algae.

The NOAA satellite imagery from June 11 shows much of the bloom is gone.

The Okeechobee Utility Authority, which relies on the lake as a primary source of drinking water, also regularly tests for microcystins and has reported no problems. The surface water plant treats water from Lake Okeechobee by coagulation, filtration, ozonation and chloramines for disinfection. The ozone takes out the color, turbidity and odor, and has the added benefit that it inactivates toxins. The EPA publication “Cyanobacteria and Cyanotoxins: Information for Drinking Water Systems” states that ozone is “very effective for oxidizing extracellular microcystin, anatoxin-a and cylindrospermopsin.”

Of the 13 water samples taken near algal blooms in the lake since the algal blooms started this summer, only one has tested above the EPA standard for recreational contact. A June 5 sample, taken about 10 miles southwest of Port Mayaca, tested 17.6 micrograms per liter. Another sample taken that same day about 5 miles from Port Mayaca showed no toxins present.

National Oceanic and Atmospheric Administration’s satellite imagery shows the blue-green algal bloom on the lake shrank dramatically between June 3 and June 11. The June 11 image is the latest image available of the lake. The satellites pass over the lake at regular intervals but sometimes cloud cover or rain means the images cannot be used to predict cyanobacteria.

The satellite imagery predicts concentrations of blue-green algae (cyanobacteria) in the water column. Algae visible in the lake is often a mix of cyanobacteria and other algae. The NOAA images cannot tell what type of cyanobacteria is present. The NOAA images cannot determine if there are toxins present. According to studies conducted on the lake, only a few of the dozen types of blue-green algae present in the lake are capable of producing toxins.

On June 17, FDEP sampled an algal bloom near Canal Point. Test results were not available at press time. The bloom was approximately 12 meters wide and was impounded against control gates on the upstream side of structure S-352.

No flow from lake to St. Lucie, minor flow to Caloosahatchee
The U.S. Army Corps of Engineers has not released any water from the lake to the St. Lucie estuary since March; since October, there have only been six weeks of limited releases to that canal.

During the dry season, lake water has been released to the Caloosahatchee River to benefit the river and maintain optimum salinity levels in the estuaries. When the lake dropped below 11 feet, flow to the Caloosahatchee was dropped to the 450 cubic feet per second, measured at the Franklin Lock, that has been set as the minimum freshwater flow required to prevent saltwater intrusion. If local basin runoff is more than enough to meet the minimum flow level at the Franklin Lock, no lake water is released.

The heavy flow at the Franklin Lock on Sunday was from local basin runoff. Flow to the river at Moore Haven averaged just 1 cubic foot per second on June 16. Flow at the Franklin Lock averaged 4,151 cfs. On Monday, flow at the Moore Haven Lock was just 4 cfs. Flow at the Franklin Lock was 3,589.

Flow at the St. Lucie Lock was also local basin runoff. Flow at the Port Mayaca Lock was 0 cfs. There has been no flow from the lake into the St. Lucie Canal since March. As of June 12, the Port Mayaca gates were closed. Earlier in the year, when the lake dropped below 12 feet, there was some backflow into the lake from the St. Lucie Canal. Flow at the St. Lucie Lock from the St. Lucie Canal into the St. Lucie River was 461 cfs. On Monday, flow at the St. Lucie lock, all from basin runoff into the St. Lucie Canal, averaged 372 cfs.

For seven-day average (June 11-17), flow from the lake west at Moore Haven averaged just 17 cfs, while flow at the Franklin Lock averaged 746 cfs. No lake water was released to the St. Lucie Canal at Port Mayaca. Flow south averaged 1,118 cfs.

During that 7 day period, the level of Lake Okeechobee rose from 10.99 feet above sea level to 11.21 feet above sea level.