Harmful algae bloom spreading across San Francisco Bay, turning water brown

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ByLiz Kreutz via KGO logo
Thursday, August 18, 2022
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Experts say a potentially harmful algae bloom called Heterosigma akashiwo is spreading in the Bay Area waters, turning it brown and murky.

SAN FRANCISCO (KGO) -- Looking out across the San Francisco Bay, you might notice it's looking a little murky.

Experts say the reason is a potentially harmful algae bloom that's spreading in waters throughout the Bay Area. It's called Heterosigma akashiwo and it's what's currently causing the water in the bay to look so dirty and brown.

"About three weeks ago, the last week of July, we started getting reports of a very unusual brown discoloration of the water," Ian Wren, a scientist with San Francisco Baykeeper, told ABC7 News. "Soon thereafter we learned the Department of Public Health had taken samples around Jack London Square and they identified the species that's causing this bloom."

Scientists at San Francisco Baykeeper, including Wren and field investigator Aundi Mevoli, are studying the algae closely. They've been taking water samples from different parts of the bay and sending them to a lab in Richmond to be analyzed. He said they have seen the algae around San Francisco, Oakland, Emeryville, Berkeley and Richmond. It's also been reported in other areas, including Lake Merritt.

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"We're not quite sure what's causing it," Wren said. "There are some physical factors that might have sparked this bloom. such as that it's been relatively clear out, the winds have died down a little bit, we have warmer waters, however, it's really hard to associate what causes this kind of bloom."

According to San Francisco Baykeeper, the last time an algae bloom of this kind occurred in the San Francisco Bay was 2004. It's unclear it's growing again now, but Wren said the nutrients polluting the bay are a major factor.

"There's about 40 wastewater treatment plants that discharge a lot of phosphorus and nitrogen into the water," Wren said. "And that's the building block for algae such as this."

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"Normally conditions are such that the bay is rather turbid, it's hard for sunlight to penetrate it, the bay is very choppy and it prevents the growth of large blooms like this," he added. "Right now we're in this situation where they really took off and we don't really know when it's going to stop."

Wren said the algae can kill shellfish and other marine life. It's not believed to be harmful to humans or pets.

"However, the cities of Alameda, Oakland, County of Alameda, East Bay Parks have issued cautionary warning postings that advise against recreating in the water," Wren said.

Wren said the way to prevent future outbreaks is to reduce the amount of nutrients flowing into the bay. He said, if not, the current conditions combined with climate change could lead to even more common -- and potentially worse -- algae outbreaks.

"It's quite conceivable that in other years a different type of species could take off and with much more harmful consequences," Wren said. "Things like higher temperatures, more nutrient upwelling from the ocean, changes in title circulation and wind patterns, these are all things that really produce a lot of unknowns but could still spark a lot of these blooms. Not just in the San Francisco Bay but throughout California."

Waste recycling and treatment wetlands are among the strategies that Wren and Mevoli believe could make a difference.

"I'm pretty discouraged," Mevoli said. "I'm hopeful with better policy we can make sure there is not too much nutrient load in the bay that would have this be a recurring event year after year."

The California Department of Public Health sent the following statement regarding the discovery of Heterosigma akashiwo:

California Department of Public Health (CDPH) staff provided consultation to the Regional Water Quality Control Board (RWQCB) at their request, and used microscopy to identify marine plankton. Presumptive identification of the abundant species of plankton was Heterosigma akashiwo, a single celled flagellate that is not known to cause human illness (but it has been documented to contribute to fish kills). A general precaution is for people and their pets to not enter the water during times of any dense blooms or discoloration in the water; however, questions regarding water quality, ecosystem health, safety, origin, extent and related concerns regarding this situation need to be addressed by the RWQCB.

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