More than 200,000 rainbow trout suffocated in a matter of minutes Tuesday at the American River Hatchery near Rancho Cordova due to an unexpected release of gunk from Folsom Dam that clogged water intakes.

The unexpected die-off could mean anglers have a tougher time finding fish to catch next year, since the 4-inch Eagle Lake subspecies of rainbow trout were to be released when they grew larger, said Bill Cox, hatchery system manager at the Department of Fish and Wildlife, which also operates the adjacent Nimbus Hatchery for salmon.

State hatchery managers already were struggling amid a disease outbreak and California’s historic four-year drought to keep enough fish in lakes and rivers to satisfy their legal obligations to supply fish for the state’s nearly 2 million recreational anglers.

“We already had less inventory than we wanted for this hatchery,” Cox said. “Now, if we lose those fish, that’s a big hit. Now, we’re going to have to figure out what we’re going to do about it.”

Cox said the die-off at the American River Hatchery occurred without warning Tuesday afternoon. He said he’s not exactly sure what happened, but he knows that the Bureau of Reclamation, which manages Folsom Dam, “changed to a pipe they hadn’t use in several years” as part of a dredging operation.

“And when they did that, a slug of stuff … came down and came into the hatchery,” he said.