Harmful algae detected in Oakland's Lake Merritt could be 'an ominous sign for the Bay'

Earlier this month, signs posted around Oakland’s Lake Merritt made some joggers stop in their tracks. “Avoid water contact,” they cautioned in bold letters. “Harmful algae may be present.” The warnings came after a mysterious red substance emerged in the water between the Lake Merritt Sailboat House and the Rotary Nature Center on March 7, as the Oaklandside first reported. Subsequent lab testing by the California Department of Public Health and San Francisco Bay Regional Water Quality Control Board last week confirmed the presence of Heterosigma akashiwo in the water — the same species of harmful algae responsible for the Bay Area-wide red tides and mass fish kills reported in 2022 and 2023.