A small dam and reservoir in Tuolumne County, California, US, has been declared stable after heavy rainfall yesterday sent a major surge of water and debris into the system, threatening the failure of the dam. The Moccasin dam functioned properly under this natural stress and at no time was there any threat to the Bay Area’s water supply, a statement from the San Francisco Public Utilities Commission (SFPUC) has said.

Early Thursday (March 22) afternoon, SFPUC activated its emergency action plan at SFPUC-owned facilities after crews observed water leaking on the downstream face of the Moccasin dam. In coordination with local officials, the SFPUC ordered an evacuation for all people who were potentially in harm’s way, including at the Moccasin Fish Hatchery and Moccasin Marina. The dam itself never overtopped and remains intact.

The water level in the Moccasin reservoir has significantly decreased since the initial incident and the SFPUC began draining the Moccasin reservoir into the much larger Don Pedro Reservoir. Crews are now actively inspecting the current state of the dam and the extent of any damage to it and its spillways.

Moccasin Reservoir is one of the SFPUC’s smallest reservoirs and is used for regulating the Hetch Hetchy water system.