Under the current proposal, Temperance Flat would slightly more than double water storage on the San Joaquin River from below Friant Dam.

The project is highly controversial because it would flood scenic canyons and historic sites along the San Joaquin River, and impact upstream hydroelectricity generation.

[2] Temperance Flat would allow the San Joaquin River reservoir system to capture significant amounts of winter and spring runoff that would otherwise be spilled downstream because of insufficient storage capacity.

Thus, the Temperance Flat Dam project would cause a net loss of hydroelectric generation, in lieu of massive reconstruction of upstream facilities.

Additionally, 240 foot tall embankment cofferdams would be built on streams surrounding the area in order to divert flows.

In their most recent draft, the Bureau of Reclamation deleted measures to construct temperature control devices on Friant Dam, which are known to improve habitat quality for salmon.

[16] Reduction of spring flood flows, via capture by Temperance Flat dam, could reduce rearing habitat for spawning salmonids downstream.

Bald eagles, several special-status bat species, ringtails, American badgers, and San Joaquin pocket mice are found in the Temperance Flat study area.

Western pond turtles, which are a California Species of Special Concern, occur regularly at several sites along the proposed flooded area.

Additionally, the California tiger salamander, is federally listed as vulnerable in this area and has designated critical habitat nearby.