Blue-Green Algae Update Contra Costa Environmental Health

2017-08 Blue Green Algae Update

Starting in summer 2015, Environmental Health has responded to citizen complaints about the presence of Harmful Algal Blooms (HABs) in Discovery Bay. The HABs toxin, microcystin, has been found in some of the water samples. In summer of 2016, Environmental Health started routine sampling in various parts of Discovery Bay instead of just conducting complaint sampling.

Discovery Bay waters were sampled for testing on June 27, 2018. The results indicate levels of cyanotoxin that exceed recommended limits. The appropriate Caution and Danger signs have been provided to the Harbor Master for posting.

Environmental Health advises residents and visitors to Discovery Bay to avoid coming into contact with water in affected areas. Avoiding contact with the water is also advised for pets. Based on the results obtained from the EPA and in accordance with state guidance, Environmental Health will post public access areas and advise residents of harmful toxin levels via social media and other electronic communication.

For a fact sheet to help veterinarians diagnose illness related blue-green algae exposure, visit

Blooms of blue-green algae, also known as cyanobacteria, can look like green, blue-green, white or brown foam or scum floating on top of water, or suspended in the water. Warm water temperatures and nutrients contribute to blooms, but these will eventually subside under cooler conditions.

CCEH will regularly test bodies of water throughout Discovery Bay and update the community while these conditions persist.

“Anyone who had contact with blue-green algae and has now developed symptoms or believes they may have consumed contaminated water should contact their healthcare provider immediately or call California Poison Control at 1-800-222-1222,” said Underwood.

No illnesses linked to Discovery Bay algae blooms have been reported in 2017. A child became sick after swimming in Discovery Bay during a similar event in 2016. Only recreational water areas are affected. Tap water in Discovery Bay is unaffected by the algae bloom.

For updates, detailed explanations of posted advisories, a map of sampling sites and other information, visit

To contact Environmental Health please call (925) 692-2500.

Thank you for your support in helping us to keep your community safe.


2 thoughts on “Blue-Green Algae Update”
    I saw this recently published news report saying, basically, “Stay out of the water” in Discovery Bay.

    That’s a CYA response by Contra Costa County and fake (exaggerated) news.

    Yes – some toxic blue-green algae was, again, tested in some stagnant end areas of Discovery Bay’s bays. It might have been here for years. But someone noticed it a couple of years ago and got the County involved. It is undoubtably worse than decades ago because of the over-exporting of water out of the Delta to send to farmers in the Central Valley. Then the pesticides and fertilizer runoff from those farms flows back into the San Joaquin River, flows north, back into the south end of the Delta, and exacerbates the problem. That’s true.

    But it doesn’t mean we are at dire risk. Paddle-boarders, kayakers, and swimmers in almost all of the Discovery Bay bays are not a risk at all. Where I live in Discovery Bay, on the east side, we have never tested positive for any toxic blue-green algae. Nor has the northern half had any toxic algae. Only at the far ends of a few bays on the southwest side has there been readings, and then mainly between the docks and the levees. To me, it’s irresponsible for the County to issue a notice like they just did. They should instead report where they have tested and found issues (like only one spot in the entire area tested “Danger”) and they should have reported how far from the shore it exists (usually only a few feet) and what to do if you see it (don’t swim through it, don’t drink it, wash your dogs off if they swim through it, etc.) Common sense warnings. Not this over-exaggerated “Stay out of the water everywhere” nonsense warning.

    If there is a great white spotted off Monterey Bay, does the state close down all of the beaches from Oregon to San Diego for the rest of the summer? Of course not. The local beach for a day and then they expect people to use common sense. And blue-green algae isn’t nearly as much a threat as a great white!

    But instead CCC issued this community-wide, damaging warning. When they did the same warning two years ago, our community lost home sales, the marina lost business because boats launched elsewhere (even though none of the algae was near the boat ramps), and marina businesses thus lost sales.

    To me, it’s irresponsible. Yes – if you see it swim around it. No – you don’t need to stay out of the water throughout most of Discovery Bay or the Delta.

    Instead, make them tell us specifically if there is any problem and where. But for everyone else, enjoy our community and enjoy your summer in the water!

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