San Luis provides water mainly for irrigation in the San Joaquin Valley, where it augments the supply for more than 1 million acres (400,000 ha) of agricultural land, although some water is also used for urban and environmental uses. The dam was built between 1963 and 1968, and filled for the first time in 1969. It provides flexibility to the state water system by capturing, via pumps and canals, the wet season (November-April) runoff that would otherwise flow from the Sacramento–San Joaquin River Delta into the Pacific Ocean. It also generates hydroelectricity by releasing the water when it is needed. However, it has indirectly impacted the environment by enabling increased water diversion from sensitive estuary regions. In recent years, a combination of drought and pumping restrictions enacted to protect endangered fish have contributed to low water levels at the San Luis Reservoir.