County closes Lake San Antonio due to mysterious, ongoing fish die-off.

On Saturday, July 6, the County of Monterey announced there was a large fish die-off at Lake San Antonio, and that officials from the California Department of Fish and Wildlife believed it was due to the heat wave—air temperatures in the area exceeded 110 degrees—which was perhaps causing a depletion of oxygen in the water. 

Last night, July 9, the county announced that it was closing the lake’s facilities indefinitely to visitors “out of abundance of caution for public health…due to a large-scale fish die-off from an unknown cause.”

County Parks staff first observed large numbers of fish washing ashore on July 5, but they were small fish, mostly baitfish like shad, the county’s statement says. But the die-off has continued, and now includes larger fish like bass, carp, catfish and trout, among others. 

And the cause of the die-off, first believed to be related to the heat—which can deplete oxygen in water—has been further thrown into question: CDFW officials tested that water and its oxygen levels came back in the normal range, and per the county’s announcement last night, “With the continued die off, especially of larger species that should not be impacted under the current environmental conditions” the county’s Environmental Health Bureau “issued a ‘precautionary measure directive’ to [County] Parks to keep the public from boating, fishing, and swimming in the lake.” (CDFW officials also collected fish samples to test, but the county’s announcement doesn’t state if any results have yet come back.)

Given that uncertainty, “County Parks staff has made the difficult decision to close the entire Lake San Antonio facility until this situation has been resolved.”

County Parks Chief Bryan Flores says in the statement, “While this may be a natural occurrence, until it is known that this is not being caused from a biological vector or pollutant that could cause harm to the public, we must keep the public safe by closing the park.”

The small number of visitors that were already camping or boating at the lake have been advised they must decamp by noon today, July 10. 

No new visitors to the lake are being admitted, and the county will advise the public once the cause of the die-off is determined, but the most immediate task is to clean up the dead fish. 

In the meantime, the county’s announcement states, “There is no estimate at this point on when clean up could be complete or reopening could occur.”