Lake San Antonio in southern Monterey County is closed to the public until further notice because a large number of fish have turned up dead and rangers don't know why.
"Yeah, we have a mystery," said Bryan Flores, Monterey County Parks Chief.
The fish die-off reportedly started the day after the Fourth of July.
Parks officials originally thought triple-digit temperatures and low oxygen in the water were causing the die-off of mostly small bait fish but deeper-dwelling fish like carp, catfish and bass also started washing up.
"It's difficult to keep people out of the water, especially on 100-degree days, and that was the fear that, you know, either dogs or people could potentially be impacted if there was something that could harm humans causing this fish die-off," Flores told KSBW reporter Felix Cortez.
County leaders made the call to shut down the park on Tuesday, forcing vacationers to pack up and leave.
"There was a couple dozen campers that were currently there, but we were sold out for this coming weekend at south shore where you can reserve campsites and then we were anticipating thousands of people coming to north shore where you don't need a reservation and can camp right along the water," Flores said.
The California Department of Fish and Wildlife, state water resources and Monterey County's environmental health department are now investigating the cause of the fish die-off.
"We're hopeful that the first part of next week we'll get some test results back that would shed some light on what's causing this, and hopefully it's not anything that would be of concern to humans and we can get the lake reopened," Flores said.
County officials say those who had reservations will be given user credits that they can use for future camping dates.
