The corps has already spent about $24 million just to determine the scope of the problems at Lake Isabella, and with the New Orleans levee failures during Hurricane Katrina a lingering memory, Congress has appropriated money for other federal dam repair projects as well.

But about two-thirds of all dams are private, and financially struggling state and local governments own most of the remainder. It is difficult to predict how needed repairs to these dams will be financed; legislation to provide federal money to help has languished in Congress. What’s more, the number of high-risk dams keeps rising as structures age, downstream development increases and more accurate information is obtained about watersheds and earthquake hazards.

Among the corps’s dams, Lake Isabella is one of 12 that are ranked in the highest category, as a dam with serious problems and serious failure consequences, given the large downstream population. “The classification is it’s an unsafe dam,” said Eric C. Halpin, the corps’s special assistant for dam and levee safety. But Mr. Halpin noted that 319 of the corps’s dams were considered “actionable from a safety standpoint.”

Lake Isabella would be one of the more expensive projects, but then again, its problems are legion. It is actually two earthen dams, a main one that is 185 feet high and an auxiliary one that sits on higher ground and is 100 feet high. With a rock ridge between them, they stretch for about a mile across the Kern River Valley.

For six decades the dams have controlled flooding on the Kern, helping Bakersfield to grow and thrive. And the lake that formed behind the dam has become the main driver of the economy of Lake Isabella and other towns, bringing fishers, boaters and whitewater rafters to the area.

But there have always been people in the area who felt the dams were flawed.

David Laughing Horse Robinson, an artist and teacher who lives in the lakeside town of Kernville, said his grandfather, who worked on the dam, and others used to talk about it. “Constantly,” he said. “How it was the stupidest thing they ever did. It’s doomed.”