Blue-green Algae and Health

Blue-green algae are microscopic organisms that can form dense blooms in surface waters. 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.

View more images of blue-green algae blooms

Avoid It

Always stay away from blooms in surface waters:

  • Don’t swim, fish, boat, or wade in areas with blooms.
  • Don’t eat fish caught from areas with blooms.

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

  • Bloom or no bloom, never drink, prepare food, cook, or make ice with untreated surface water.
  • During a bloom, don’t drink, prepare food, cook, or make ice with surface water, even if you treat the water yourself. Also, consider not using it for showering, bathing, or washing.

If you are on public water:

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

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