OROVILLE (AP) — State engineers on Thursday discovered new damage to the Oroville Dam spillway in Northern California, the tallest in the United States.

Earlier this week, chunks of concrete went flying off the emergency spillway, creating a 200-foot-long, 30-foot-deep hole.

Department of Water Resources spokesman Doug Carlson said officials will ramp up the outflow from the damaged site Thursday so officials can drain Lake Oroville.

Meanwhile, reservoir levels continued to climb behind the critical flood-control structure. Officials said it is at 90 percent of its capacity. They said the dam is still safe and doesn’t threaten communities downstream.

“The integrity of the dam is not jeopardized in any way because the problem is with the spillway and not the dam,” said Eric See, a spokesman for the Department of Water Resources.

As a contingency, state officials are preparing to use the emergency spillway at the dam.

Crews have been clearing trees, rocks, and other debris from the hillside near the dam where water will flow.

Lake Oroville would naturally flow over this ungated concrete crest, into a mostly unlined emergency spillway if the reservoir reaches 901 feet elevation. This would be the first time the spillway has been used in the dam’s 48-year history although the reservoir came within 1 foot of flowing over in January 1997.

Meanwhile, workers at a state hatchery for California’s native Chinook salmon loaded up all the baby salmon into tanker trucks Thursday afternoon to try to save them from the mud, concrete chunks and other debris coming their way from the crumbling spillway.

The hatchery, on the Feather River, is vital to the survival of the state’s native chinook salmon, whose numbers have dwindled during the drought. Hatchery managers planned to take the tiny young salmon to another holding point they hoped was far enough away.

Lake Oroville, in Butte County, is a central piece of California’s government-run water delivery network. It is used to supply water, generate electricity and for flood control.