Thousands of fish carcasses have been floating up to the edges of the San Francisco Bay, and the scummy top of Oakland’s Lake Merritt – stewing under the sun and wafting a putrid stench into nearby neighborhoods.
The dead bat rays, striped bass, sturgeon, anchovies and clams, are probably mass victims of an algal bloom that scientists are racing to understand. In the meantime citizen scientists, local photographers, joggers and naturalists have been capturing dramatic photos of the die-off.
“The diversity of life in Lake Merritt is just incredible,” said Damon Tighe, a naturalist who documents wildlife in the lake, a unique ecosystem in Oakland, California, that contains both fresh and saltwater. A range of fish, crustaceans and mollusks call the lake home as do large breeding populations of herons, egrets, geese and ducks. Salmon, sturgeon, jellyfish and leopard sharks have also navigated into the lake in recent years.
The die-off in the lake is probably due to an algal bloom of Heterosigma akashiwo, which was first spotted at various points across the San Francisco Bay and estuaries in late July. The alga is likely sucking up all the dissolved oxygen in the water, leaving the fish to asphyxiate, said Jon Rosenfield, a scientist with the San Francisco Baykeeper conservation group, which has been tracking the phenomenon. Heterosigma akashiwo also produces a toxin that may have killed the fish.
The result is ruddy, brown-tinged water – slopping into shores along with thousands of bloated fish bodies. According to the San Francisco Bay Regional Water Quality Control Board, algae density measured on 10 August were the highest observed in more than 40 years.
Massive fish die off going on right now in Lake Merritt #oakland #fish #lakemerritt
— Damon Tighe (@damontighe) August 28, 2022
May be related to the HUGE algal bloom that’s been happening on the east bay since the start of the month in front of Alameda where effluent flows…https://t.co/1H1byxoWOk pic.twitter.com/kU5pH55KVC
The deaths of sturgeon in parts of the San Francisco Bay have been especially striking, given that the fish are so large, and armored against many environmental threats. The fish can live for decades.
“This is like losing giant redwoods,” Tighe said. “I don’t think people quite understand the significance – this is really big.”
Researchers are also conducting tests to investigate what might have caused the bloom. Effluent water from wastewater treatment plants is probably to blame, according to Rosenfield.
“Researchers have known for decades that the levels in this estuary are really high,” he said. “In fact, many have wondered why this hasn’t happened yet.” Existing wastewater systems were not designed to filter out the phosphorus and nitrogen that leads to such red tide algae blooms, he added. “This is a problem society as a whole has ignored for too long.”
Officials have suggested that decreased water flow from estuaries to the ocean, due to the statewide drought, may also have contributed.
As the Bay Area braces for a brutal heatwave in the coming week, Rosenfield said the warm temperatures could exacerbate the bloom, depending on whether or not it has already passed its peak. The heat could also further cook the carcasses and worsen the stench. Crews in Oakland have begun cleaning up the dead fish in anticipation of hotter temperatures through the holiday weekend.
“I worry about how long this will last and what the longer impacts will be,” said Tighe, noting that many birds feed on the lake’s fish. “This could cause big ripple effects.”
In 1870, Lake Merritt became the first protected wildlife refuge in America. In recent years, local officials have been working to restore its water quality and clear it of built-up trash.
The Associated Press contributed to this story
