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Blue-Green Algae


Blue-green algae, also known as cyanobacteria, are simple organisms found naturally in water and wet environments. Blue-green algae prefer warm, stagnant, nutrient-rich water and are found most often in ponds, lakes and slow-moving rivers.

A blue-green algae bloom is a buildup of algae that creates a green, blue-green, white or brown coloring on the surface of the water, sometimes occurring as mats or scum. They can occur at any time but are most common between June and September. Blue-green algae blooms are increasing in occurrence not only in California but nationwide as well.

Some species of blue-green algae produce toxins, so skin contact and ingestion can be dangerous. Children and pets are at the greatest risk of serious toxic effects from blue-green algae.

Exposure to water containing toxic blue-green algae, for example by direct body contact or ingestion, can result in a number of symptoms including the following:

  • rashes
  • eye, nose, mouth or throat irritation
  • allergic reactions
  • headache
  • gastrointestinal upset including abdominal pain, nausea, vomiting and diarrhea
  • malaise

How to Avoid Toxic Exposure

Follow these steps to protect yourself and those around you:

  • Always assume that a blue-green algal bloom is toxic.
  • Do not swim and avoid jet-skiing, wind surfing or water skiing in water with scum layers or blooms.
  • Do not allow children or pets to swim in water with scum layers or blooms.
  • Do not drink or use blue-green algae water. Boiling will not remove algal toxins.
  • If you come into contact with a bloom, wash your skin and hair thoroughly. If wearing a swimsuit, pay careful attention to skin under the swimsuit.
  • If your pet comes into contact with a bloom, wash it thoroughly with clean water to prevent blue-green algae ingestion while your pet cleans itself. If you believe your pet may have ingested dry or liquid algae contact a licensed veterinarian right away.
  • Do not eat fish or shellfish caught or harvested in a bloom area.
  • Respect any water-body closures by public health authorities.
  • If you ingest blue-green algae or suspect that you may have and begin to experience symptoms, contact your health care provider or California Poison Control 1-800-222-1222.