Harmful Blue-Green Algae Blooms

Blue-green algae are microscopic organisms that can form dense blooms in surface waters and on rocks and shorelines. People and animals should avoid blooms because blue-green algae can cause health effects.

Know It

It might be a blue-green algae bloom in surface water if you see:

  • Strongly colored water (blue-green, green, yellow, white, brown, purple, or red).
  • Paint-like appearance.
  • Floating mats or scums.

images of harmful blue-green algae blooms

Blooms can also form on rocks, along the shoreline, and at the bottom of a waterbody. These are called benthic blooms.

images of benthic blooms

Avoid It

Always stay away from surface water and benthic blooms. View DEC's list of reported blooms:

  • Don’t swim, fish, boat, or wade in areas with blooms.
  • Don’t eat fish caught from areas with blooms.
  • Rinse with clean water if you, your family or pets have contact with blooms.
  • Pet and livestock illness/deaths can happen if animals consume large amounts of water containing blooms, scums or benthic mats. Immediately seek veterinarian care if noticing any symptoms in your animals. Learn more.

If you are not on a public water supply and are using surface water:

  • Bloom or no bloom, never drink, prepare food, or make ice with untreated surface water. You may also consider not using it for washing, especially if it looks cloudy.
  • During a bloom, don’t drink, prepare food, or make ice with surface water, even if you treat the water yourself.
  • Boiling water will not remove blue-green algae or their toxins. Learn more.

If you are on public water:

  • Your water is treated, disinfected and monitored for drinking and household use. Learn more.

Report It

  • Report blooms to: the DEC
  • Report blue-green algae related symptoms to: your local health department
  • Consider visiting a healthcare provider if you, your family, or your animals are experiencing symptoms related to blue-green algae blooms. Symptoms include diarrhea, nausea, or vomiting; skin, eye, or throat irritation; and allergic reactions or breathing difficulties.

HABs at Beaches

HABs at Water Supplies

Learn More