A Bay Area Algae Bloom Killed Hundreds of Sturgeon. A New Study Just Tallied the Damage.

Before the numbers below mean anything, it helps to know where they came from. A new study didn't count a fish kill in San Francisco Bay in real time with agency biologists on boats. It reconstructed one after the fact, using a scattered pile of iNaturalist posts, tips to conservation groups, and agency hotline calls, because the event itself moved faster than anyone was prepared to track. That matters for reading what follows: every number here is very likely a floor, not a ceiling.

What actually happened was a San Francisco Bay algae bloom fish kill that started in July 2022, when a bloom of the algae Heterosigma akashiwo began in a man-made lagoon and spread across more than 4,500 square kilometers of open water in the San Francisco Estuary. It triggered a mass die-off touching bony fish, sharks, rays, crustaceans, mollusks, worms, and jellyfish, including the estuary's southernmost spawning populations of White Sturgeon and the federally threatened Green Sturgeon.

What They Found

Researchers pulled together 401 public sighting reports and 14 formal agency reports, covering roughly 7,900 individual dead organisms across 25 families, including 18 fish species. Sturgeon carcasses totaled 691: 200 confirmed White Sturgeon, 16 confirmed Green Sturgeon, and 475 too far gone to identify to species. Striped bass turned up in even higher numbers, 1,981 carcasses, and yellowfin goby weren't far behind at 1,371. Observers covered 98 sites across 13 subregions of the Bay, though on average they only managed to survey about 32 percent of the accessible shoreline. Confirmed White Sturgeon ranged from 68 to 213 centimeters, averaging 145. Chlorophyll-a levels, tracked as a measure of the bloom itself, peaked on August 22 and were back to baseline by September 1. More than half the total carcasses had been logged by August 28, and 90 percent by August 31, several days before the water even turned severely low-oxygen on September 5. The researchers point to that timing as the reason they think the algae's toxicity, not the low oxygen that followed it, was the main thing killing sturgeon.

How They Documented It

There's no getting around the fact that this is citizen science data, not a designed survey, and the researchers say so plainly. Reports skewed toward accessible urban shoreline and away from open water or hard-to-reach habitat. Sturgeon are bottom-oriented fish, and a dead one is more likely to sink out of sight than wash up somewhere a person would spot it. The dataset has duplicate entries, misidentifications, and a built-in bias toward big, easy-to-recognize animals over small or cryptic ones. The paper is explicit that its mortality figures are conservative lower bounds, not real counts, and that its broader estimates carry enough uncertainty that they shouldn't be read as precise.

Fishing the Bay After an Algae Bloom Fish Kill

I don't fish San Francisco Bay myself. I'm car-free and based in Dublin, most of my fishing time goes to Sierra Nevada trout water or trips back to the family cabin in the UP, and I've never targeted striped bass or sturgeon. But this happened close enough to home that it's worth sitting with. The study's own authors frame this as a call for better real-time monitoring and faster agency response, and I'd rather pass that along straight than dress it up. What stands out to me as a non-expert on this particular water is how much of what we know about a big fish kill can hinge on regular people posting photos, and how much can still slip through the cracks even then. If you do fish the Bay for striped bass or sturgeon and hadn't heard about this 2022 event, it's a reasonable thing to ask your local bait shop or a fisheries contact about, especially around late-summer conditions.

Citation

Hobbs, J. A., Sellheim, K., Sweeney, J. K., Stompe, D. K., Kelly, J. T., Ervin, J., Willmes, M., Rosenfield, J. A., Wren, I., Mevoli, A., Senn, D. B., Odkins, K., Rinde, J., Tighe, D., & Lewis, L. S. (2026). Mass mortality of aquatic organisms in the San Francisco Estuary, using community science to document the impacts of a severe harmful algal bloom. Frontiers in Marine Science, 13, 1893110. https://doi.org/10.3389/fmars.2026.1893110