California Lake Closes As Officials Investigate Mass Fish Die-Off

Lake San Antonio in Monterey County, California, has been closed to the public amid investigations into the vast numbers of dead fish washing up on the lake’s shores over the course of several days.

Monterey County officials first announced a “large fish death event” in a July 6 social media post , noting that the California Department of Fish and Wildlife had been notified. At that time, the cause of death was believed to be the result of “extreme temperature change, causing oxygen depletion in the water” with California recently having been hit by a record-breaking heatwave .

The lake remained open, with officials stating they did not believe there was any risk to humans or their pets, but visitors were cautioned to leave the dead fish alone.

But on July 10, Lake San Antonio was forced to shut to visitors.

“The fish die off we alerted you to last Friday has gotten worse,” said county officials in a Facebook post , “and the lake is being closed as a public health precaution while testing and clean up is being done.”

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Fish ranging in size from small baitfish through to larger catfish, bass, and trout could be seen floating in the lake’s waters and washing ashore, attracting scavenging birds and maggots. “It seems like every fish species in the lake is being impacted,” Chief of Parks Bryan Flores told SFGATE . “We have never seen this type of multi-species die-off, especially on this scale.”

While previously suspected as having something to do with the sweltering temperatures, the cause of the mass die-off is now being treated as unknown until investigations provide further information.

“We’re waiting on reports back from the Department of Fish and Wildlife, Water Resources Agency, and Health Department to determine what the cause of this massive fish die-off is,” said Flores in a video posted to Facebook .

But the official does have some ideas of what may or may not be behind the event, which he believes could have been spontaneous and unlikely to have a more nefarious source.

“If it was a poison, you’d think it would be impacting the other species,” Flores explained to KRON4 . “More than likely, it is some kind of biological process that’s occurring, whether or not it’s algae or protozoa.”

Until that theory is or isn’t confirmed, however, the lake remains closed indefinitely.

In a statement seen by the San Francisco Chronicle , Flores said: “While this may be a natural occurrence, until it is known that this is not being caused by a biological vector or pollutant that could cause harm to the public, we must keep the public safe by closing the park.”