Credit: Dr. Gerry Pinto, Doctors Lake in Clay County

Nutrient overload, or eutrophication, from too much nitrogen and phosphorous is one of the most serious water quality problems facing the St. Johns River and its tributaries.

Blue green algae, also called cyanobacteria, are tiny organisms naturally found in all types of water. Excessive nutrients feed the cyanobacteria, causing uncontrolled algal blooms that deplete oxygen in the water needed by fish and reduce light that is essential to submerged vegetation. Some types of cyanobacteria produce toxins that can be harmful to the health of humans, pets, and wildlife.

Different types of algal toxins include hepatotoxins (toxins that damage the liver), dermatoxins (toxins that damage the skin) and neurotoxins (toxins that damage the nerve cells).  The World Health Organization (WHO) and many states have adopted recreational guidelines to inform the public of health risks associated with exposure to cyanobacteria and their toxins.  Unfortunately, Florida is not one of them.  The U.S. Environmental Protection agency (EPA) also recently issued draft criteria and swimming guidelines. 

The St. Johns suffers from an excess of nutrients from wastewater treatment plants, industrial discharges, failing septic tanks, storm water runoff, and fertilizers that regularly wash into the river.

  • Blooms can look like a thick mat or foamy green scum and can give off an unpleasant odor.
  • Blue green algae sometimes produce toxins that can result in ear, eye, or skin reactions and hay fever-like or flu-like symptoms.
  • Do not swallow, swim, or wade in water where blooms are present.
  • Do not eat fish caught in the vicinity of a bloom.
  • Wash your skin and clothing with soap and water if you come into contact with a bloom.
  • Keep pets away from blooms.

If you see an algal bloom, please report it to St. Johns Riverkeeper and to the Florida Department of Environmental Protection by visiting the toll-free hotline at 855-305-3903.  When possible, also include GPS coordinates and photos. 

To report illnesses or symptoms from being exposed to a toxic algal bloom, contact the Florida Poison Control Center at
1-800-222-1222.  For information on health advisories, contact your local county health department.

For more helpful information about algal blooms and how to avoid exposure to potentially harmful toxins, visit the following website:

Blue Green Algae FAQ from the Florida Department of Health

Aquatic Toxins – Florida Department of Health

Algae and Cyanobacteria – GreenWater Laboratories

Blue-Green Algae – Florida Fish and Wildlife Conservation Commission