Health Services

Cyanobacteria (Blue-Green Algae)

Cyanobacteria, also known as blue-green algae, are microscopic organisms found in marine and fresh water environments. They are usually present in low numbers, but under favorable conditions of sunlight, temperature, and nutrient concentrations, can form massive blooms that discolor the water and often result in a scums and floating mats on the water’s surface. Some species of cyanobacteria produce toxins that can cause health problems in humans and animals if exposed to large enough quantities.

Frequently Asked Questions

Are all Cyanobacteria toxic?
No. There are many species of Cyanobacteria, many of which are non-toxic. Moreover, species that are known to be toxic may only be toxic at certain times within a bloom when environmental conditions are optimal.

What are typical routes of exposure to Cyanobacteria?
People can be exposed to cyanobacteria and cyanotoxins by swallowing the water, by skin contact with the water and/or the surface scum, or when airborne droplets containing toxins are inhaled while swimming.

What are the human health risks associated with exposure to Cyanobacteria?
Any reaction to cyanobacteria exposure will depend on the type of species and toxin present, the toxin concentration, and the duration of the exposure. The higher the concentration of cyanobacteria and toxin and the longer the contact with the water, the more severe the symptoms may be. Health effects typically occur only when exposed to high levels of cyanobacteria and/or their toxins, although some people may be sensitive to lower levels.

Skin contact with the organisms can cause irritation of the skin (rash or skin blisters), eyes, nose and throat, and inflammation of the respiratory tract. Swallowing water containing high levels of toxin can lead to nausea, vomiting, abdominal pain and diarrhea. Effects on the liver and nervous system of animals and people have also been documented in severe cases. Livestock and pet deaths have occurred after these animals consumed large amounts of algal scum that had accumulated along shorelines.

Are some individuals more at risk?
Yes. Children and individuals with liver disease, kidney damage, or weakened immune systems may be at greater risk. Children have a greater opportunity for exposure to Cyanobacteria blooms, since they tend to be curious and may explore the shoreline of a lake. Because children tend to swallow a greater volume of water per body weight than adults, they also have a greater potential risk from exposures to blooms.

How can you tell if waters contain Cyanobacteria?
People should suspect that blue-green algae could be present in water that is visibly discolored or that has surface scums. Colors can include shades of green, blue-green, yellow, brown or red. Water affected by blue-green algal blooms may also develop a paint-like appearance. Contact with waters that appear scummy, turbid or discolored, should be avoided.

What should I do if I think I swam in waters containing Cyanobacteria?
The first step is to wash with warm soapy water. Remove clothing to avoid contact with trapped algal cells, as these may cause skin irritations. If any of the above exposure symptoms develop, contact your physician immediately. In any event, please alert the Suffolk County Department of Health Services at (631) 852-5760.

What should I do if I think I my pet entered waters containing Cyanobacteria?
Wash your pet with warm soapy water, and if any of the above exposure symptoms occur, contact your Veterinarian. Also, please alert the Suffolk County Department of Health Services at (631)-852-5760. 


New York State Department of Health: Blue-Green Algae Information Bulletin
World Health Organization (WHO) Cyanobacteria Guide
Center for Disease Control (CDC), Facts about Cyanobacteria 
Monitoring of Toxic Cyanobacteria in Suffolk County Lakes (C. Gobler, 2007)