Incursions of saline water into the Sacramento-San Joaquin River Delta from the San Francisco Bay has been a concern since the 1870s.

[3] In 1988, voters approved funding of the Los Vaqueros Reservoir project to begin design and construction.

In addition to building the $61 million, 192-foot-tall dam, the district had to: In March, 2010, CCWD approved a capacity increase of 60,000 acre-feet (74,000,000 m3).

Barnard subcontracted Reinforced Earth Company (RECo) to design and supply the MSE walls using its proprietary GeoMega™ MSE wall system, which utilizes precast concrete facing panels with GeoStrap® (high tenacity polymeric strips) as soil reinforcements.

[a] RECo also provided the precast concrete barrier and coping segments atop the newly expanded dam, reducing both cost and construction time for completion.

Heavy rains in the watershed since October 2016, increased the level to more than 133,700 acre-feet (164,900,000 m3) at the end of January 2017, the all-time record for the reservoir.

It also reported that six environmental groups had written a letter of support for the proposed expansion to the California Water Commission.

[9] By 2024, the estimated cost of the expansion had increased to nearly $1.6 billion, and the California Department of Fish and Wildlife updated the relevant permit for drawing water from the reservoir, making the requirements stricter.

The Los Vaqueros watershed has been preserved as 19,300 acres (78 km2) of protected open space surrounding the 1,500-acre (6.1 km2) reservoir.

[12] Other benefits of the reservoir include water storage for drought or emergencies, a protected open space, and recreation.

An additional expansion of Los Vaqueros to a capacity of 275,000 acre-feet (339,000,000 m3) is again being discussed by CCWD and other water agencies in Northern California.

[14] According to CCWD, the other public agencies that are involved as partners in current planning for the Phase III expansion are:[15] Another benefit of the watershed is the protection of nearly 20,000 acres (81 km2) of wildlife habitat in Eastern Contra Costa County.

The watershed is home for many rare, threatened and endangered species including fairy shrimp, bald and golden eagles, Alameda whipsnake, western pond turtle, California tiger salamander, California red-legged frog, San Joaquin kit fox, and the San Francisco dusky-footed wood rat.

As of February 17, 2017, seven of the trails on the Los Vaqueros property have been temporarily closed to protect possible golden eagle nests.

The south entrance is off of Vasco Road, north of Livermore and leads to the marina area and four fishing piers.