Signs posted warning of harmful algae blooms at San Gregorio State Beach

Still image of algal bloom taken from video posted on

Signs have been posted at San Gregorio State Beach near Half Moon Bay warning people of toxic algae in the creek and lagoon there, San Mateo County officials said Friday.

The algal blooms, which have toxins that are potentially fatal to people and pets, are prompting the county's Environmental Health Services to recommend that people avoid the water and banks of the lagoon and creek upstream for a quarter-mile, as well as any standing or slow-moving water with visible signs of algae growth.

The next sampling of the water in the area will be in mid-August, according to the county. 

"Harmful algal blooms can be very dangerous," Environmental Health Services director Heather Forshey said in a statement. "As families enjoy the water this summer, we urge everyone to be especially mindful of children and pets near any body of water where there is visible algae."

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More information about the harmful algal blooms can be found online at