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Is That Algal Bloom On My Favorite Pond Harmful?

RIDEM and RI Department of Health (DOH) collaborate to ensure the safety of your fishing experience. During the summer, fall, and winter months, when water levels are low and temperatures are high, RI DOH scientists sample bodies of water for blue-green algae (Cyanobacteria) toxins. If toxin levels exceed safety thresholds, warnings are issued, and signs are posted to advise against recreational activities in that body of water. Here's more information about Cyanobacteria:

What is Cyanobacteria?

Cyanobacteria, also known as blue-green algae, naturally occurs in freshwater systems. Elevated temperatures and excess sunlight can trigger algal "blooms," which have the potential to produce toxins harmful to both humans and animals. Toxins are released as the algae begin to die off or are ingested.

Identifying a Blue-Green Algal Bloom

Blooms typically occur in late summer or early fall when water levels are low and temperatures are high. While there are no visual signs indicating that a blue-green algae bloom is producing harmful toxins, identifying an algae bloom may help avoid exposure. Blue-green algae blooms are usually bright green or blue-green but can also appear brown, red, or purple. The water may appear cloudy and emit an odor. While the color of the algal bloom serves as a clue, confirmation of blue-green algae requires microscopic examination. Water samples should be tested for toxin presence.

Health Risks

Contact with blue-green algae toxins can lead to rashes, blisters, hives, and nose and eye irritation in humans. Ingesting the toxins can cause diarrhea, vomiting, or neurotoxicity (numb lips, tingling fingers and toes, dizziness). Pets or livestock that consume Cyanobacteria toxins may experience sickness, paralysis, or death. Neurotoxicity in animals manifests as salivation, weakness, staggering, difficulty breathing, and convulsions.

Avoiding Cyanobacteria Toxins

Follow all posted signs and avoid drinking, swimming, or fishing in affected water bodies. Refrain from contact with discolored water or water with surface scum. Do not consume untreated water, regardless of the presence of algae blooms.

State Measures to Reduce Exposure

Not all species of blue-green algae produce toxins, and those that do may not always release them. 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 detected, a press release and advisory are issued, and signage is posted at affected ponds. RIDEM will refrain from stocking affected ponds with trout.

Where to Get More Information

For further details, visit RI Department of Health's Harmful Algal Blooms page.

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