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Press Release

Discovery Bay Water Samples Test Positive for Algae Toxin

Wednesday, August 10, 2016

Archived. This is an older press release from 2016 and may not contain the latest information. Please view our current press releases for 2023 items.

Samples taken from the waters around the Discovery Bay community have tested positive for microcystin, a potentially harmful toxin produced by certain algal species, according to laboratory results from the U.S. Environmental Protection Agency (EPA) lab in Richmond.

Contra Costa Health Services' Environmental Health Division (CCHSEH) and the California State Water Resources Control Board (State Water Board) recommend that people, pets and livestock avoid contact with water around Discovery Bay until further notice.

The community's tap water is not affected and is safe to use.

"We received multiple complaints from Discovery Bay and we sampled those areas for blue-green algae. Test results indicate the presence of toxin and we're asking the community to stay out of the water until further notice," said Marilyn Underwood, Director of CCHSEH.

In accordance with state guidance, the level of toxin present is enough to trigger the posting of "Caution" and "Danger" signs.

"It is important for people to understand that sampling did not take place in all areas of Discovery Bay. Bloom conditions can change rapidly and we recommend minimizing contact with the water and algae in Discovery Bay," said Beverley Anderson-Abbs, an environmental scientist with the State Water Board.

The State Water Board warns against handling dried blue-green algae, removing algae from the water or attempting to treat the algae. Exposure to blue-green algae can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects on people.

"Microcystins were measured above state health-based trigger levels in eight of the ten samples," said Underwood. "Samples from Harbor Bay and three of the four samples taken from the southwest area had levels that exceed the danger level. Other areas sampled had levels that exceed the caution level or did not contain microcystin at a level of concern," said Underwood.

A map of the areas sampled and their results is available online at along with information about blue-green algae and the caution and danger signs.

"Dogs are especially vulnerable to getting sick from exposure to toxic algae blooms and there have been reports in the past of dogs dying after exposure to water with blue-green algae blooms," said Anderson-Abbs.

CCHEHS is working with Contra Costa County Supervisor Mary Piepho's office the Discovery Bay Community Services District and Reclamation District 800 to address the issue and inform the public and to post caution and danger signs in the community.

State health officials, including the California Department of Public Health, the Office of Environmental Health Hazard Assessment, and the State Water Board, have been working with local authorities to ensure that accurate caution and danger messages are available to post where needed in the community.

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  • Vicky Balladares,
    Contra Costa Health Services,
  • Sue McConnell,
    Central Valley Water Board,