Toxic Algae Found in San Gregorio Creek Lagoon: Beach Goers Advised to Avoid

South San Francisco, CA  July 1, 2022 Press Release


NOTE: The 4th of July weekend holiday leads many people to the coast to enjoy recreational activities, hence we are sharing this advisory as a heads up to all.

San Gregorio creek


Users of San Gregorio State Beach should avoid the creek, as the algae presents serious health risks

Water sampling at San Gregorio State Beach near Half Moon Bay has revealed the presence of toxic algae in San Gregorio Creek lagoon. In coordination with the San Francisco Bay Quality Control Board, San Mateo County’s Environmental Health Services has posted notices in publicly accessible areas of the state beach, warning users not to enter the creek or allow children or pets to do so.

Harmful algal blooms (HABs) produce toxins that are potentially fatal to people, pets, and livestock. The compounds produced by bacteria in the algae can cause numerous health effects in humans and animals that range from stomach pain to nerve damage and, in some circumstances, death.

Testing in San Gregorio Creek lagoon revealed the presence of algal mats, which are a type of bloom that grows on bottom surfaces. These mats can be attached to the bottom or become detached and float in the water or on the surface and wash up on shore.

The waters and banks of San Gregorio State Beach lagoon and the creek upstream for a quarter mile should be avoided due to risks from the algae. While testing occurs regularly on beaches and adjacent bodies of water, with warnings posted, any standing or slow moving fresh or brackish water with visible signs of algae growth should be avoided this summer.

Adults and children should not touch, eat, or swallow any algal mats. Dogs should not eat algal mats or drink from the water (dogs are not permitted on San Gregorio State Beach). Call a doctor or veterinarian immediately if a person or pet becomes sick after coming into contact with or ingesting algae or water from San Gregorio Creek or elsewhere where algae is visible.

More information about harmful algal blooms is available here:

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