Authorities in Northern California, worried that damage to the emergency spillway at the Oroville Dam might lead to the flooding of communities downstream, ordered the evacuation on Sunday of 188,000 people from several counties downstream.
The dam on Lake Oroville is 7,000 feet across and 770 feet high, making it the tallest dam in the United States. It has been a wet winter, and after days of heavy rain, the lake is full. The main spillway that gets water out of the lake is damaged, and on Sunday, authorities found that the emergency spillway also has a hole in it; they became concerned that if the erosion continues, it could result in "large, uncontrolled releases of water from Lake Oroville." Butte County Sheriff Kory Honea said the evacuations were ordered because he would rather "be safe than sorry."
Officials say the dam itself, 75 miles north of Sacramento, is still intact, and helicopters are dropping rocks to try to plug the hole in the emergency spillway. More rain is expected in the area on Wednesday.