Recently, the Florida Department of Health (FDOH) issued a Health Alert due to the presence of harmful blue-green algal toxins, or cyanotoxins, in the St. Johns River.

The FDOH issued the alert based on a water sample taken from the St. Johns River near Mandarin Point by the Florida Department of Environmental Protection (FDEP) on July 27, 2021. The sample had trace levels (.55 parts per billion – ppb) of the algal toxin microcystin.

The Environmental Protection Agency’s Recommended Human Health Recreational Ambient Water Quality Criteria or Swimming Advisories limit is currently 8 ppb total microcystins.

In response, St. Johns RIVERKEEPER, in conjunction with a Jacksonville University (JU) professor and graduate student, and the FDEP followed up by taking additional samples on Wednesday, August 4.

The FDEP detected no cyanotoxins in their samples taken at Mandarin Point and the end of Oakvale Road in St. Johns County.

Greenwater Labs MC Report 8.4.21 for the samples taken by JU and St. Johns RIVERKEEPER detected .31 ppb of microcystins at Mandarin Point and none at the end of Oakvale Road.

“The good news is that the concentration of toxins in recent samples were well within the recommended range for safe recreational use of our river,” explains Jimmy Orth, Executive Director of St. Johns RIVERKEEPER. “However, these results only provide a snapshot in time.  Conditions in the river constantly change that can affect cyanobacteria or blue-green algae growth and the concentrations of toxins emitted.”

While cyanobacteria, aka blue-green algae is naturally present in our waterways, excessive nutrients from fertilizers, manure, industrial wastewater, and failing septic tanks can stimulate the growth of toxic algae blooms.

Algae blooms block sunlight from reaching submerged aquatic plants and clog fish gills. As blooms die and decompose, oxygen levels are depleted causing fish kills. They can also produce harmful toxins.

“As these microscopic organisms multiply, they can form what we call an “algal bloom.” Some species of microorganisms present in a bloom can produce toxins that are harmful to marine life, pets, and humans,” explains Laura Kostrzewski, the JU marine biology graduate student who collected the samples for St. Johns RIVERKEEPER. “These toxins can be very dangerous depending on concentration levels and pathways of exposure.”


Toxins produced by the blooms can cause rashes, stomach cramps, nausea, diarrhea, and respiratory irritation. High exposure to toxins can affect the liver and nervous system. If skin contact occurs, wash off immediately and thoroughly with clean water and soap. Long-term exposure can potentially result in nerve or liver damage.

Pet owners should prevent their pets from drinking or swimming in bodies of water where algal blooms are present. Ingestion of algal toxins can cause an animal to become extremely ill. If contact occurs, rinse off immediately and keep them from licking their fur.

Kostrzewski continues, “In our samples, multiple species of toxin-producing cyanobacteria were detected. Although the toxin level was low, it suggests the need to monitor our waterways more often.”

If citizens spot what looks like bright green, paint-like scum on the surface of the water, they should steer clear. Do not recreate, boat, swim, or fish near an algae bloom.

If you encounter an algae bloom, report it to the FDEP by calling 855-305-3903 or completing an online form.

Dr. Melinda Simmons, Assistant Professor of Marine Science at Jacksonville University, advises the public on additional ways to help: “Each of us can do our part by limiting the amount of fertilizer we are using on our lawns – especially during the rainy season, pick up animal waste, and use reclaimed water responsibly. All of these things can help reduce nutrient pollution in our waterways, reducing the likelihood of blooms occurring.”