California's Oroville Dam Overflowing

Nearly 200,000 people have evacuated their homes near Oroville, California, after the spillway on the Oroville dam began to erode Sunday.

The Oroville Dam, the tallest dam in the United States, is still intact, but high waters caused the emergency spillway to begin to erode, prompting the evacuation.

In the worst case scenario, one official said, an uncontrolled release from the dam could send a 30-foot wall of water downstream.

"I'm not going to lift the evacuation order until I have a better idea of what that means and what risk that poses," Butte County Sheriff Kory Honea said in a news conference late Sunday night.

Heavy rainfall and runoff from the Sierra Nevada mountains has caused the water level in Lake Oroville to rise massively, causing the dam failure. In 48 years, the dam has never had to use the emergency spillway, until last Sunday.

So far, no repairs have been made to either the primary or emergency spillway as crews have been unable to reach them. According to authorities, the main spillway is releasing water at 100,000 cubic feet per second in an effort to reduce the amount of water traveling down the emergency spillway. Normal flows down the main spillway are about 55,000 cubic feet per second.

"The goal is to get the lake to drop 50 feet. If we can continue to do that, that brings a little bit of calm to what we're trying to accomplish here," said Kevin Lawson, California Fire incident commander.

As for the evacuated residents, they will just have to wait, and with more rain in the forecast for Wednesday, the wait could be even longer.