Toxic algal bloom found near Stuart

OKEECHOBEE — An algal bloom at the St. Lucie Lock on July 5 had high levels of the toxin, microcystin according to the Florida Department of Environmental Protection (FDEP). The test indicated microcystin levels of 154.38 micrograms per liter. The World Health Organization considers levels above 10 micrograms per liter as potentially unsafe for recreational contact. Microcystis aeruginosa, a cyanobacterium, was the dominant species in the bloom.

The bloom was described as “bright green and covers the entire visible surface of the canal. The bloom does not appear to extend down into the water column.”

On July 9, Stuart mayor Kelli Glass Leighton declared a local emergency due to the increased algal blooms occurring within the waters of the City of Stuart, including the St. Lucie River, its tributaries and connected canals.

Coastal residents fear a repeat of the 2016 Treasure Coast algal blooms, which resulted in beach closures. Contrary to the widespread misconception that periodic discharges from Lake Okeechobee alone produced the 2016 harmful algal blooms, a study by Florida Atlantic University’s Harbor Branch provided multiple lines of evidence that nutrient sources in the local basins, including on-site sewage and septic systems, contaminated the St. Lucie Estuary, in particular its urbanized sections as well as its watershed. Results of the study were published in the journal “Harmful Algae.” The study found that local basin runoff was significantly higher in nitrogen than the freshwater from the lake.
Lake releases in 2018

In 2018, no water from Lake Okeechobee was released to the St. Lucie from the lake prior to or during the month of May. All of the water entering the St. Lucie and Caloosahatchee estuaries in May was from local basin runoff. In some areas rainfall was four times the average for that month.

On June 1, the U.S. Army Corps of Engineers began releasing water from Lake Okeechobee to the C-44 canal (aka the St. Lucie canal). From June 1 to June 21, the target flow, measured at the St. Lucie Lock, was 1,800 cubic feet per second (cfs). This flow was a mixture of lake releases and direct local watershed runoff which flows into the C-44 canal.

The C-44 has a local drainage basin of 185 square miles.

From the Port Mayaca lock on Lake Okeechobee, the C-44 canal runs 23.7 miles to the St. Lucie Lock. The distance from the St. Lucie lock to the ocean is another 15.1 miles, for a total of 38.8 miles of waterway that carries a flow of local basin runoff and direct rainfall as well as any water released from Lake Okeechobee.

On June 22, the flow for the St. Lucie estuary was reduced to a seven-day average of 1,170 cfs as measured at St. Lucie Lock & Dam (S-80) near Stuart.

On June 29, the flow from the lake to the St. Lucie was reduced to an average flow of just 585 cfs, measured at the St. Lucie Lock.

The Corps halted releases from the lake to the St. Lucie canal on June 30.

No water from the lake has been released to the St. Lucie canal in July.

Tests in samples from the lake itself have shown no toxins or very low levels of toxins.

A sample taken from the lake water near Port Mayaca on July 5 had levels of 4 micrograms per liter of microcystin. A sample taken on the lake side of the Port Mayaca lock had barely detectable levels of 0.31 micrograms per liter microcystin.

A sample taken lakeside at the Port Mayaca Lock on July 2 showed low levels of toxin with 1.9 micrograms per liter of microcystin.

Tests on lake samples taken July 9 are not yet available.

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