May 31, 1969, the San Luis Reservoir filled for the first time. In 1981, during low water conditions in San Luis Reservoir, a long segment of the upstream face of the dam partially collapsed, causing of material to fall into the reservoir. Since the reservoir was at a low level the dam was in no immediate danger of failure, however it could not be safely refilled until the damage was repaired. By August 1982, the area had been stabilized with of additional fill (known as a "buttressing berm"), at a cost of $6.1 million. In July 1984 another crack appeared in the dam, but it soon stabilized. Water supply Most of the water stored behind San Luis Dam is used for irrigation. The CVP share of the water is released down the Delta-Mendota Canal into the San Joaquin River, which provides water for of farmland in the central part of the San Joaquin Valley. Parts of the CVP and SWP water supply the Westlands Water District of Fresno and Kings Counties, which irrigates up to of land on the west side of the San Joaquin Valley. Prior to the construction of San Luis Dam and the joint use portion of the California Aqueduct (the San Luis Canal) this area depended entirely on groundwater. In 2016 the main crops grown here were almonds, tomatoes, pistachios and wheat. Most of the Westlands district consists of large corporate farms totaling hundreds if not thousands of acres. The SWP also provides more than of water per year for farmers in Kern County. San Luis Reservoir stores water for the Metropolitan Water District of Southern California (MWD) which is one of the primary providers of water for the Greater Los Angeles Area. This water reaches Southern California via the East and West Branches of the California Aqueduct. It also provides water for the Central Coast cities like San Luis Obispo and Santa Barbara via the Coastal Branch of the California Aqueduct. Local water agencies and irrigation districts are allowed to "bank" water in San Luis Reservoir for later use, by purchasing it during the rainy season at lower prices when it is not immediately needed. However, regulations only allow such carryover storage when San Luis is not full, since state and federal water takes priority. Once the reservoir fills, any carryover water that has not been used is effectively "lost", i.e. transferred to the CVP