blue-green algae

The Discovery Bay Community Foundation (DBCF) has formed a harmful algae bloom (HAB) subcommittee, partnering with agencies across the state to help mitigate the epidemic.

Blue-green algae is a hot topic in Discovery Bay.

While some residents are unconcerned each summer as the algae’s trademark scum appears atop stagnant water in the bays around town, many are worried about the algal blooms’ toxic effects. The Discovery Bay Community Foundation (DBCF) has formed a harmful algae bloom (HAB) subcommittee, partnering with agencies across the state to help mitigate the epidemic.

“This team includes top cyanobacteria scientists from around the state, including scientists from UC Davis, USC, several water districts and water board personal,” said DBCF founder Jim Mattison. “I reached out to ... see if they could help us figure out what we can do with our stagnant 32 bays that are now very bad.”

Since 2017, the foundation has worked with these entities to ascertain why the algae has become a significant issue in the last four years. Each month, Mattison takes a team of scientists from the Department of Water Resources (DWR) around the town’s bays to take water samples. And he believes they’ve identified the root cause of the blooms’ recent escalations.

“We’ve been around the 32 bays, and we know the main culprit are the fertilizers from the central valley farmers that end up in the Delta,” Mattison said. “They contain large amounts of nitrates and phosphates.”

The fertilizers feed the algae, and when the right conditions are met — warm, still, shallow water — the algae begin blooming, releasing microcystins, a toxin harmful to humans and animals.

Mattison explained the subcommittee has applied and been approved for a state grant to conduct a load study to find out where and how the fertilizers and nutrients are entering the Discovery Bay waterways. He said there are still hurdles before funds are received, but expects a plan will be devised to neutralize the fertilizers in the water.

Mattison suspects the solution will include a hydrogen peroxide-based component to strip the oxygen off the cyanobacteria and help stop the toxic HAB. Anything they come up with, however, will still require approval from state agencies like U.S. Fish and Wildlife, the Contra Costa Agriculture Department and several others.

Joe Doser, supervising environmentalist for Contra Costa County, sees the results of the DWR’s monthly testing. In a recent email to The Press, he said the town’s bays all look clear, but there was a caution level of toxins at the mouth of Kellogg Creek on July 31.

“With one exception, we’re still getting good results,” Doser said. “All the results, except for near the discharge point of Kellogg Creek, came back within safe limits ... In the vicinity of the Kellogg Creek discharge point, South Newport Drive, a ‘Caution Level’ warning is recommended.”

The algae usually bloom in shallow, stagnant, nutrient-rich water after consecutive days of high temperatures. While these conditions usually come to a head during August, fast-moving water isn’t affected. Residents may notice the trademark green, white or brown foam, or “scum” that indicates algae blooms floating in the waters near and under their docks as the summer progresses. In still, warm water with plenty of nutrients, the scum can float on top of or lay suspended in the water.  

Pets are especially susceptible to these toxins because they are more likely to ingest water while swimming. Pay attention to signage posted around the bays to know if it is safe to swim.

Water safety and quality don’t fall under the Town of Discovery Bay’s jurisdiction. In a previous interview with The Press, general manager Mike Davies said he and his staff will fully cooperate with the county in an effort to keep residents safe and informed.

“Although the town of Discovery Bay is not responsible for water quality in the Delta, we do provide information and referral resources on our website when we receive updates on blue-green algae conditions in our area,” Davies said.

For information on the county’s samples from July 31, or to learn more about HAB, visit the Contra Costa Environmental Health page at To see information posted by the town of Discovery Bay, visit