Mammoth Pool Reservoir is a reservoir on the San Joaquin River in the Sierra Nevada, within the Sierra National Forest in California. It creates the border between Fresno County and Madera County. It is about 45 miles (72 km) north-northeast of Fresno.

The 123,000 acre⋅ft (152,000,000 m) reservoir is formed by Mammoth Pool Dam, an earth-fill dam completed in 1960. It was built by Southern California Edison for hydroelectricity production. The dam's power plant can produce up to 190 megawatts. The dam, reservoir and power plant are part of the Big Creek Hydroelectric Project, perhaps the most extensive hydroelectric system in the world.

The reservoir is also a recreation area. Activities at the lake include, swimming, fishing, camping and boating.

The reservoir is closed to the public during the month of May and the first half of June to allow migrating deer to swim across the reservoir so as to spend the summer in the Sierra Nevada highlands.

The reservoir is inaccessible following the first snowstorm, usually occurring in November, as the access road is not snowplowed.

Road access to a campground beside the reservoir was blocked by the Creek Fire on 5 September 2020, at which point officials recommended that campers wade into the reservoir for their own protection. Many were later evacuated by helicopter.

• List of dams and reservoirs in California
• List of lakes in California

• SCE Big Creek Hydro
• Yosemite/Madera County Film - Mammoth Pool Pictures
• Aerial Image at Panoramio