Update: Contra Costa County Provides Information on Discovery Bay Blue-Green Algae


On August 3, Contra Costa County Health Services issued an update after testing was performed regarding blue-green algae.

According to the County, they say in July, Environmental Health inspectors, responding to multiple citizen complaints, sampled areas of Discovery Bay for blue-green algae. Preliminary field tests indicated the presence of potentially harmful blue-green algae and people in Discovery Bay were advised to avoid playing in bodies of water in the area.

Samples were taken throughout the Discovery Bay community and were sent to labs run by the U.S. Environmental Protection Agency (EPA) and the California Department of Public Health in Richmond.

The EPA tests for total microcystin, a potentially harmful toxin produced by certain algal species. Based on the results obtained from the EPA, our Environmental Health Division has posted Caution and Danger advisories in affected areas (see map). Environmental Health is also working with the community to get advisories to areas that are not accessible by the public.


Is it safe for me to go in the water in Discovery Bay?

It depends where you are and if there are advisories posted in the area.

A CAUTION sign means:

  • Do not swim or wade near algae or scum
  • Keep your children away from algae in the water or on the shore
  • Do not drink the water or use it for cooking
  • Do not let pets or livestock go into or drink the water or eat scum on the shoreline
  • Do not eat shellfish from the water


A DANGER sign means:

  • Stay out of the water until further notice. Do not touch scum in the water or on shore.
  • Do not let pets or livestock drink or go into the water or go near the scum
  • Do not eat fish or shellfish from these waters
  • Do not use the water for drinking or cooking. Boiling or filtering will not make the water safe.


Exposure to blue-green algae can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects. At high levels, exposure can result in serious illness or death, according to the California Department of Public Health.

What about my pets?

Keep pets out of water with blue-green algae blooms. Dogs are especially vulnerable to getting sick and there have been reports through the years of dogs dying following exposure associated with drinking the water and licking algae from their fur after wading/swimming in water with blue-green algae blooms.

Is there an issue with drinking water?

No, contamination only affects recreational water areas, not drinking water from the tap in Discovery Bay.

Who should I contact if I swam in the water and now have symptoms?

If you think you or someone else is displaying symptoms of blue-green algae poisoning, contact your health care provider or the California Poison Center Help Hotline at 1-800-222-1222.




  1. Hello Discovery Bay,

    Sounds like you have a problem with scum in your waters. Here in Antioch we have an abundance of scum floating around our streets and neighborhoods.

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