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Rhode Island

Freshwater Fishing

Freshwater Fishing

Algal Bloom

Is That Algal Bloom On My Favorite Pond Harmful?

RIDEM and RI Department of Health (DOH) are working together to keep your fishing experience safe. During the summer, fall and into the winter months, when the water levels are low and temperatures are high, RI DOH scientists sample bodies of water for blue-green algae (also known as Cyanobacteria) toxins. If toxin levels are too high, warnings are issued and signs are posted to refrain from recreational activities on that particular body of water. Here is a little more information about Cyanobacteria:

What is Cyanobacteria?

Cyanobacteria is a blue-green algae that occurs naturally in freshwater systems. High temperatures and excess sunlight can lead to algal ‘blooms’ which have the potential to produce toxins that are harmful to both human and animals. The toxins are released when the algae begin to die off or are ingested.

How do you identify a blue-green algal bloom?

Blooms generally occur in late summer or early fall when the water level is low and water temperature is high. There are no visual signs that a blue-green algae bloom is producing the harmful toxins; however, identifying an algae bloom may help you avoid the chance of exposure. Blue-green algae blooms are normally bright green or blue green in color, but can also be brown, red or purple. Water may appear cloudy and may produce an odor. The color of the algal bloom is a clue; however, confirmation of blue-green algae can only be identified using a microscope. Water samples should be tested for toxin presence.

What are the health risks?

Humans who come in contact with the blue-green algae toxins can develop rashes, blisters, hives, and nose and eye irritation. If swallowed, humans may experience diarrhea, vomiting, or neurotoxicity (numb lips, tingling fingers and toes, dizziness). Pets or livestock that ingest the Cyanobacteria toxins can experience sickness, paralysis and even death. Neurotoxicity in animals is characterized by salivation, weakness, staggering, difficulty breathing, and convulsions.

What can you do to avoid Cyanobacteria toxins?

Adhere to all posted signs. Do not drink, swim, or fish in affected water bodies. Avoid contact with water that is discolored or has scum on the surface. Do not drink untreated water, whether algae blooms are present or not.

What does the state do to reduce human/pet exposure to the Cyanobacteria toxins?

Not all species of blue-green algae produce toxins and the blue-green algae that can produce the toxins may not. Toxins can be detected through laboratory tests. Water testing is conducted throughout the summer and results are reported to RI Department of Health and RIDEM. If toxins are found, a press release and advisory is issued and signage is posted at the pond. RIDEM will not stock affected ponds with trout.

Where can I get more information?

For more information, visit