top of page

Red tide invading peninsula waters not toxic, experts say

A red tide is seen in the San Francisco Bay from Paradise Drive overlooking the Richmond-San Rafael Bridge. Experts have identified the red-brown algae as Heterosigma akashiwo and say it’s not toxic but still advise people to stay out of the water where it’s blooming. (Cindy Siciliano photo)

Water-quality-control experts say a mysterious red algae bloom that invaded the waters off Tiburon and Belvedere last week is harmless, but they advised staying out of the water just the same.

Eileen White, executive officer of the San Francisco Regional Water Quality Control Board, said water samples collected off the Tiburon ferry terminal and Sausalito marina on Aug. 18 were found to contain Heterosigma akashiwo, a microscopic marine algae that can turn water red-brown.

“The good news is that this is not harmful to people,” White said, “it’s just ugly.”

However, out of “an abundance of caution,” White suggested people refrain from swimming when the bloom was present. “Some people do have sensitivities, and it might cause skin irritation,” she said.

For the complete story, pick up this week's edition of The Ark on newsstands or SUBSCRIBE NOW for home delivery and our e-edition.



Recent stories

Support The Ark’s commitment to high-impact community journalism.

The Ark, twice named the nation's best small community weekly, is dedicated to delivering investigative, accountability journalism with a mission to increase civic engagement and participation by providing the knowledge that can help sculpt the community and change lives. Your support makes this possible.

In addition to subscribing to The Ark for weekly home delivery, please consider making a contribution to support independent local journalism. For more information, contact Publisher & Advertising Director Henriette Corn at or 415-435-1190.​

bottom of page