Lake Oroville and its dam in Northern California are critical components in California’s complex water-delivery system. Damage to spillways that are used to drop water levels in the lake and relieve pressure on the dam prompted evacuation orders covering nearly 200,000 people. Here’s a look at Lake Oroville and its place in California’s water system: How important is Lake Oroville? Lake Oroville is the starting point for California’s State Water Project, which provides drinking water to 23 million of the state’s 39 million people and irrigates 750,000 acres of farms.