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Wastewater, Not Climate, Fueled Massive Algae Bloom in ‘Epicenter of Supposed Environmentalism’ of San Francisco


It was late July when San Francisco Bay Area residents first grew concerned: the water in a channel near Oakland was turning a murky, tea-colored brown.

Scientists in the region tested the water and found a bloom of algae, Heterosigma akashiwo, that causes a form of what is known as “red tide.” By the end of the August, the bloom had spread throughout the San Francisco Bay. Observers who flew over the bay saw that most of the water had turned a reddish brown. And then came the fish kills: dead sharks, sturgeon, stiped bass, minnows, and other sea life washed up and covered local shores.

The algae bloom was the worst in the San Francisco Bay in almost two decades.

Warm water is typically one of the key ingredients algae blooms need to grow, so many people likely assumed that scientists, environmental activists, and mainstream media outlets would point at climate change as the primary cause of the San Francisco Bay bloom. But that’s not the case. In a report earlier this month, the San Francisco Chronicle confirmed that what fueled the bloom was not a mystery, and it wasn’t the warm weather. Rather, the bloom was fueled by excessive nutrients in the wastewater, or effluent, pumped into the bay by the region’s 37 sewage plants.

“Either you’re treating the effluent to standards that are safe for the receiving waters or you’re not. It doesn’t have anything to do with the climate. Either you have working infrastructure or you don’t. You’re either overflowing raw sewage or you aren’t,” said Kristi Diener, a California clean water advocate, who is also an advocate for the state’s farmers and ranchers.

Diener said the algae bloom and the fish kills, which have since dissipated, caused the Bay Area’s eight million residents and its leaders to wake up to the long-brewing problem. San Francisco Bay has among the highest nutrient levels of any bay or estuary in the world.

Burke said it’s an oversimplification to say the San Francisco Bay bloom was fueled by “poop and pee” as the Chronicle did – the sewage plants aren’t pumping untreated human waste into the bay. But for the most part the nutrients do come from human waste – “poop water, how’s that?” Burke said. The sewage plants, she said, aren’t doing anything illegal.

“Their permits allow them to do what they do,” she said. “What the rest of us are saying is those permits need to be reevaluated, and they need to be held to a higher standard.”

Rosenfield and other scientists suspect that a generally warming climate, combined with increasing nutrient loads, could be part of the reason why algae blooms are becoming more common globally. But, he said, in the Bay Area, the temperature algae needs to form a bloom is exceeded under normal conditions, and “has been for decades.” And while California’s drought is affecting river flows, the impact that has on the San Francisco Bay is typically felt more in the winter and spring, he said. So, while climate change could be helping to set the table for more blooms generally – and it may have helped to trigger this summer’s bloom in San Francisco – the massive bloom “could have happened without climate change, and it’s been predicted for three decades,” Rosenfield said.

Burke was blunt about what happened in the Bay Area this summer: “It’s about nutrient load. And the nutrient load is coming directly from wastewater treatment plants.”