[5] Envisioned as early as 1919 as an effort to conserve, control, store, and distribute water to the Central Valley, California's main agricultural region, Shasta was first authorized in the 1930s as a state undertaking.

However, bonds did not sell due to the onset of the Great Depression and Shasta was transferred to the federal Bureau of Reclamation as a public works project.

Even before its dedication, Shasta Dam served an important role in World War II providing electricity to California factories, and still plays a vital part in the management of state water resources today.

[7] The low-lying topography of the Sacramento Valley makes it vulnerable to flooding in the winter; conversely, irrigation is necessary during the summer due to the highly seasonal precipitation.

This caused water shortages for Delta farms, and led to a teredo (saltwater worm) infestation between 1919 and 1924 that destroyed piers and ships in Suisun Bay.

[10] In a bid to solve the salinity problem, local residents proposed constructing a tidal barrage across the mouth of Suisun Bay, a project which was never realized.

The dam would store water for release during the dry months when the Delta was most vulnerable to saltwater intrusion, with the added benefit of controlling floods in the winter.

[12][13] The Marshall Plan was not widely supported due to its high cost (about $800 million in 2008 dollars); when proposed to Congress in 1921, it passed in the Senate but failed in the House of Representatives.

However, the 1930s were a time of economic crisis with the onset of the Great Depression and a severe drought that devastated the agricultural sector, pushing the unemployment rate in California up to 20 percent.

The project was approved in the state legislature by a slim margin, mostly riding on Central and Northern California voters, who needed both the jobs and the water.

Southern California generally opposed the project because they needed money to build an aqueduct to the Colorado River, from which the state had previously secured rights.

The construction works at Shasta Dam and other parts of the project would provide thousands of much-needed jobs, contributing a major portion of the Depression era federal job-creation programs.

The bridge was built to a height of more than 500 feet (150 m) above the Pit River, some 7 miles (11 km) east-northeast of the dam site, to accommodate the rising waters of Shasta Lake.

[24] The bypassed segment of the railroad from Redding to the Shasta site was re-appropriated as a branch line for construction trains, and was routed through a tunnel beneath the south abutment of the dam.

Toyon served purely to provide housing for Reclamation personnel, government offices, and storage; no stores or restaurants were permitted within its boundaries.

[18] Using this system, construction crews were able to transport concrete from the mixing plant, which lay directly adjacent to the main tower at the end of the conveyor belt, to the rising structure of the dam faster and cheaper than any other method.

[37] The dam played an important part in World War II even before its completion, supplying much-needed electricity to shipyards and aircraft factories in central California.

[51] The expansion is considered feasible because the dam's foundations were originally built to carry the weight of an 800-foot (240 m) structure, but resources shortages at the onset of World War II prevented completing it to that final design height.

[52] The "low option", which simply comprises adding a vertical concrete dike to the top of the dam, would provide maximum additional storage while minimizing requirements for reconstruction of buildings and facilities around Shasta Lake.

The "intermediate option" would require adding more than 100 feet (30 m) to the crest and replacing the elevator towers on the front of the dam, and the Pit River Bridge and small towns around the lake, if not modified or moved, would be inundated.

[54] Opponents of dam raise contend that it would cost more (starting with replacing over 600 structures that would be inundated under the lake including the Pit River Bridge) than its benefits.

[58] However, Westlands has had a spotty record with environmental responsibility and has been criticized by environmentalists for high levels of pesticide and selenium in the toxic runoff waters from farms operating under the district.

The massive structure completely prevents salmon migration from the lower reaches of the river to the Upper Sacramento, Pit, McCloud and other tributary streams.

Warm waters are harmful to salmon, which prefer colder temperatures, and also impact other fish populations such as steelhead and wild California trout.

[62][63] In an attempt to save the plunging salmon populations, the federal government constructed the Coleman National Fish Hatchery on Battle Creek in 1942.

The hatchery is situated approximately 20 miles (32 km) southeast of Redding, and produces 13,850,000 eggs per year – nearly 87 percent of which are for the fall chinook salmon run.

[64] Another remedy was carried out by the Bureau of Reclamation in 1991, with the installation of a gigantic facility called a TCD (Temperature Control Device) on the rear face of Shasta Dam.

[65] The dam has vastly reduced the amount of sediment in the Sacramento, and the riverbanks now suffer decreased erosion, slowing the growth of meanders and side-channels.

Tribal members argue that several reservation treaties originally set by the U.S. government in the 1850s were later broken so the filling of Shasta Lake could proceed; afterwards, only a tiny fraction of that land remained theirs.

Many public and private marinas, campgrounds, RV parks, resorts and boat launches border the reservoir, one of the most popular recreational lakes in California.