Warm temperatures and little water movement continue to set the stage of algal blooms in Florida lakes, rivers and canals.

At the Pahokee marina, a toxic blue-green algae bloom first reported April 9 appears to be under control. Water sampled April 9 showed microcystin toxin levels of 12 parts per billion (ppb). The World Health Organization considers levels above 8 ppb to be unsafe for human recreational contact (swimming) and levels above 1ppb to be unsafe for drinking water.  City of Pahokee staff used algaecide to break up the bloom. The following week, toxin levels had dropped to 2 ppb. The most recent tests showed toxin levels of 1.1 ppb.

According to the Florida Department of Environmental Protection (FDEP) April 25 report, National Oceanic and Atmospheric Administration (NOAA) satellite imagery showed low to moderate bloom potential on approximately 50% of Lake Okeechobee, mostly along shorelines and the northern part of the lake. The imagery varies from day to day, and algae conditions on Lake O can change from one hour to the next.

“Bloom potential” does not always mean visible algae. The satellite imagery detects chlorophyll levels. According to information shared at Florida Blue-Green Algae Task Force meetings, other biological matter in Lake O could impact these readings. Also, of the 28 species of cyanobacteria (commonly called blue-green algae) only about 25% are capable of producing toxins and those that can produce toxins do not always do so. While scientists are still studying what causes toxin production, studies have found higher toxin levels in water with higher levels of dissolved nitrogen.  (Toxic algal blooms in coastal waters were linked to nitrogen in runoff from septic tanks.)

FDEP samples water statewide where algal blooms are reported.

For the week of April 19-25, FDEP conducted 26 reported site visits in Florida. Algal bloom conditions were observed by samplers at 13 sites. Most samples did not have detectable toxins.

Trace levels of microcystin toxins (0.34 ppb) were found in the Caloosahatchee River North Canal Circle. Algae there were mixed with no dominate taxon.

Trace levels were also found in Lake Arnold on the north shore -- 0.16 ppb microcystins and 0.38 ppb anatoxin-a.

On April 23, South Florida Water Management District sampling found trace levels (0.10 ppb) clylindrospermopsin in the C-51 canal in Palm Beach County.

SFWMD also found trace levels (0.53 ppb) of microcystins at the Fellsmere Water Management Center. Woronichinia naegeliana was the dominant taxon.

SFWMD samples from Lake Jesup had trace levels (0.21) cylindrospermopsin detected with Cylindrospermopsis raciborskii and Planktolyngbya limnetica co-dominant.

On April 23, Highlands County staff collected two algal bloom samples. An algal bloom at the Lake Placid boat ramp was dominant for Cylindrospermopsis raciborskii; no cyanotoxins were detected.  At the Lake Glenada boat ramp, Microcystis aeruginosa and Microcystis wesenbergii were co-dominant, with trace levels of 0.47 ppb microcystins detected. 

Because you cannot tell what species of algae and/or cyanobacteria are present without laboratory testing and you cannot tell if toxins are present without laboratory testing, the Florida Department of Health advises the public to avoid all areas with visible algal blooms. Do not allow pets near water where algae are visible. Do not consume shellfish from areas where visible algal blooms are present. Fish caught in waters with algal blooms are safe to eat, according to FDOH, if you rinse the fillets with clean water. Do not consume fish livers, warns FDOH, as any toxins will be concentrated in the liver.