Built of local rock, the dam was an 800-foot (240 m) long, 6-foot (1.8 m) tall structure designed to divert water for the irrigation of 250,000 acres (100,000 ha).

[7] Friant Dam was originally proposed in the 1930s as a main feature of the Central Valley Project (CVP), a federal water project that would involve building an expansive system of dams and canals on the rivers of the Central Valley to provide water for agriculture, with secondary purposes of flood control, municipal supply, and hydroelectric power generation.

In the middle of the Great Depression, the Friant Dam site saw a huge influx of job seekers, many of whom had to live further away in surrounding cities.

Before any concrete was laid on the dam's main wall, the underlying rock was extensively grouted to fill in 725 holes and seams that might otherwise cause instability in the foundation.

In summer 1941, the labor force reached a peak of 1,500, and the monthly record for concrete placement, at 228,000 cubic yards (174,000 m3), was set in August.

However, the spillway gates, the water release valves and the two irrigation canals Friant was intended to support remained unfinished in the wake of the WPB's order.

Less than a year later, the WPB "[determined] the completion of the Madera Canal and the installation of valves at the Friant Dam, necessary for war-time food and fiber production" – allowing construction to resume on a limited scale.

[11] A pair of control valves were borrowed from Hoover Dam, allowing the closure of the river outlets and Millerton Lake began to fill on February 21, 1944.

This is a line of creation, built to unlock the fertility of the rich soil, to resist drought, to overcome floods, to provide outdoor recreation, and to generate cheap power that will improve the living conditions of millions of our citizens.

[16] The dam is operated to maintain a flow of 6,500 cubic feet per second (180 m3/s) or less on the San Joaquin River at Mendota, 60 miles (97 km) downriver.

However, large snowmelt floods often exceed the capacity of the dam and reservoir and force larger releases downstream, potentially causing damage to riverside property and infrastructure.

The desiccation of the river has caused the degradation of large stretches of riverside habitat and marshes, and has nearly eliminated the historic chinook salmon run that once numbered "possibly in the range of 200,000 to 500,000 spawners annually".

[23] Reduction in flows has also increased the concentration of pesticide and fertilizer runoff in the river contributing to pollution that has further impacted aquatic species.