Blue-Green Algae

Childing Jumping in LakeGo Jump in the Lake, but Look Before You Leap!

Blue-green algae (cyanobacteria) are naturally-occurring bacteria that live in ponds, lakes, rivers and streams across our state. Sunny weather causes them to grow. Blue-green algae thrive in shallow, undisturbed, surface waters. Large amounts of algae can discolor water and form floating scums on the surface. Water may look greenish, yellowish or even brownish red. Severely affected water may take on a paint-like appearance.


Toxic Algae Skin ReactionSome types of blue-green algae produce toxins (poisons) that are dangerous to animals and humans. Contact with toxins can cause skin, eye, nose, and throat irritation. If swallowed, they can harm the liver and nervous system of both humans and animals. Humans should avoid exposure to blue-green algae and should protect their pets and livestock from exposure, as well. Some animals have died after ingesting large amounts of floating scum.

Symptoms of Toxin Exposure

  • Allergic reactions
  • Breathing difficulties
  • Skin, eye, nose, and throat irritation

If you develop symptoms of toxin exposure after swimming, bathing, or showering stop using the water and seek medical attention.

Using Lakes Safely

  • Swimming, bathing and showering with water that is not visibly affected is usually considered safe.
  • Avoid contact with water that appears discolored or has surface scums. Prevent pets and livestock from contact, as well. If contact occurs, wash area with soap and clean water.
  • Do not drink surface water, regardless of whether algae is present. In addition to algal toxins, surface water can harbor other types of organisms that make people sick.
  • If you use surface water in your home, find out if blue-green algae have been reported in your water source.
  • If you wash dishes with surface water, wearing gloves and rinsing dishes with bottled water may lessen exposure risk.
  • Blue-green algal toxins cannot be detected by the water's taste or odor.
  • Home treatments (boiling, filtering, UV light, and chlorine) do not deactivate toxins.

Blue-Green Algae in Lake WaterWater Testing

Testing lake water may not be the best way to determine if water is safe on a particular day. In the days between sample collection and testing, an algal bloom can dissolve or be carried to another part of the lake by currents or wind. It is more effective to simply look for blooms and scums before using or entering the water. Humans should avoid contact (swimming, drinking, bathing, etc.) with water that appears discolored or has surface scums.

Email the NY Harmful Algae Bloom (HAB) to report any blooms outside of the monitoring season. Include lake name, location, and photograph of HAB with your email.