Almaden Reservoir is an artificial lake in the hills south of San Jose, California in the United States.

It borders on the 4,163-acre (1,685 ha) Almaden Quicksilver County Park,[7] which provides limited fishing[8] ("catch-and-release"), picnicking, hiking, and horseback riding activities.

The California Office of Environmental Health Hazard Assessment has issued a "Do Not Eat" advisory for any fish caught in Almaden Reservoir due to elevated levels of mercury.

Its waters reach the San Francisco Bay by way of the Guadalupe River.

It is one of the smaller reservoirs owned by the Santa Clara Valley Water District.