Photo by Tony Kukulich. Algae blooms are seen here in the water near Windward Point in Discovery Bay. The area has received a danger advisory from the county following toxicity tests late last month. 

Blue-green algae, otherwise known as cyanobacteria, has once again reared its scummy head in the waters of Discovery Bay, and at least one state agency is working to learn more about it.

On May 2, a group of Central Valley Regional Water Quality Control Board (CVRWQCB) staff members took samples from Discovery Bay waters for a nutrient-loading assessment study, according to an email from environmental scientist Christine Joab.

“During the sampling, staff noted small clumps of visible cyanobacteria at three of the sampling locations,” Joab stated in her email. “These locations were the yacht harbor near the Boardwalk Grill, Pebble Bay along the deep channel, and at the mouth of Discovery Bay and Indian Slough.”

A sample collected from the yacht harbor was brought back to a lab for cell identification, and cyanobacteria was dominant in the sample. However, Joab added that the amount of cyanobacteria was low, and no toxin testing was performed.

The Contra Costa County Environmental Health department tested local waters for toxins in February. Supervising Environmental Health Specialist Joe Doser said all samples came back at safe levels.

“The only detectable cyanotoxins were by the fuel pump in the yacht harbor, but this was still at a safe level,” Doser said. “When the weather gets warm again, Environmental Health will collect samples. The harmful algal blooms tend to occur during warmer weather.”

Due to recent rains and cooler temperatures, harmful blooms are not currently a concern. Once temperatures have been higher for some time — usually in August — residents will start to notice large areas of scum on the water surface. When this happens, the county advises residents and their pets to steer clear of the scum to avoid the illness that can follow exposure to the toxins.

The CVRWQCB is part of the California Environmental Protection Agency, and its mission is to protect water quality and all the benefits and uses of water. Staff members will continue collecting monthly samples as part of the nutrient-loading study. Sue McConnell, one of the board’s staff members, explained that the agency is conducting the load study to gather more information on the water, the algae blooms and everything else going on in the Delta.

“We are doing some testing to get more information on what’s going on in Discovery Bay,” McConnell said. “We didn’t do testing for toxins, so we don’t really know, but visually, there was a small amount of cyanobacteria observed.”

Mike Davies, general manager for the town of Discovery Bay, said that while water safety and quality don’t fall under the town’s jurisdiction, 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.

To learn how to protect yourself from harmful algal blooms, visit For information on the CVRWQCB, call (916) 464-3291 or visit For information on the county’s samples from February, visit the Contra Costa Environmental Health page at To see information posted by the town of Discovery Bay, visit