Blue-Green Algae Has Returned to Discovery Bay


On Tuesday, Town Manager Mike Davies announced that the Town of Discovery Bay was informed by Contra Costa Environmental Health that Blue-Green Algae has returned to Discovery Bay.

CCEH has issued a health advisory and supplied signs to the Harbor Master for posting.

The following was released by the Town of Discovery Bay:

Photo provided by Town of Discovery Bay

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.


  1. I was out paddle boarding in the Delta about a week and a half ago……was sick for the next three days. Coincidence? 🤔

  2. I believe there was a warning not to swim in those waters there a few months back because of water quality issues in the delta near DB. They need to hone in on the problem soon if people are getting sick.

    • Yes, I was unaware of that warning or I would definitely not have gone paddle boarding. I didn’t swim, but I am still not feeling well and on antibiotics.

  3. How do we know what areas are affected. I live at the north end of Willow lake which has been ineffected in the past but I would like to see the testing map for 2018.

  4. I hate to say it because, really, the county needs to just issue a warning year ’round to not go in the water. Peroid; but folks really should just know that the water is toxic and stay away. This is a classic “employer not protecting the worker” line which is why I hate it, but come on people… This has been going on the last how many years now? This was an oversight by the builder and lack of waterflow is the root problem. It seemed like a good idea when it was built but not working out so well these days. It’s a shame and I do feel bad for the folks that are affected I have a great idea: let’s do the *SAME THING* in Bethel Island….

  5. The real tragedy for DB waters are those tunnels. If it’s bad now you haven’t seen anything yet. After the tunnels all those little bays will be swamps. Stop the tunnels. We don’t want DB to be a ghost town when it ruins the bay fronts.

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