The emergency spillway helps to ensure that the water does not rush over the top of the dam when the levels are high. Though the dam remains intact, the spillway is eroding.
The damage prompted a mandatory evacuation for cities and counties near Lake Oroville amid fears it could endanger communities living downstream. Butte County Sheriff Kory Honea said the order remained in effect, but said he had no idea when it would be lifted.
"I'm not going to lift the evacuation order until I have a better idea of what that means and what risk that poses," he said in a press conference late Sunday night.
A state emergency order was issued by California Governor Jerry Brown to help authorities with the situation and evacuations.
Heavy rainfall has filled Lake Oroville this winter to the verge of overflow, and the Lake also gets additional water from the northern Sierra Nevada mountain range which is experiencing one of its wettest seasons.
The Dam provides flood control for the region and is located about 75 miles north of Sacramento. The dam has two spillways; the primary and the emergency spillway to prevent that from happening. These channels leak water out of the lake, and currently, both have major problems.
According to the California Department of Water Resources, the primary spillway was damaged by erosion as photos were released showing a massive hole on the lower part of the structure.