Aerial view looking south of wetlands on Sherman Island and San Joaquin River background, both part of the Sacramento-San Joaquin River Delta in Sacramento County, California. Photo taken March 08, 2019.

January 16, 2025 - What’s New: In December 2024, a new framework took effect to minimize harm to endangered species from the operation of California’s two biggest water projects. The framework, developed by federal fishery agencies and called a “biological opinion,” replaces a framework that had been in place since 2019.  

How It Helps the State Water Project: The new science and additional flexibility that underpin the revised framework allow water project operators to respond more nimbly to real-time conditions in California rivers and the Sacramento-San Joaquin Delta, where rivers drain to San Francisco Bay. Farms and cities have the potential to gain additional water supply, while endangered species are protected. 

Why It Matters: The State Water Project, a network of reservoirs and pumping plants, provides some or all of the water used by 27 million Californians and 750,000 acres of farmland. Since the new biological opinion went into effect on December 19, the State Water Project – a major source of Southern California water supply – already has gained 12,500 acre-feet of additional water supply beyond what would have been possible under the 2019 framework. The additional supply is approximately enough water to meet the needs of 37,500 households for a year.   

Framework Requirements: The new federal species-protection framework, as well as a new state permit issued in November 2024, require the State Water Project to cut back pumping in the winter when certain waterways in the central Delta become turbid, or cloudy with sediment. This action is required to avoid drawing endangered Delta smelt toward the State Water Project pumps that lift water into canals for delivery to other regions. (Cloudy water allows smelt to hide from predators.) Slowing the water project pumps when turbidity rises allows the State Water Project to avoid entraining smelt, which would trigger even deeper curtailments in pumping. 

Latest Operations: High winds in the Delta this week raised turbidity in central Delta channels, so the State Water Project and the federal Central Valley Project will slow pumping for at least two days, depending upon turbidity levels. About 6,400 acre-feet of water could be foregone as water supply if the pumping slow-down lasts five days, which is about .29% of the amount of water the State Water Project supplies a year, on average. Starting January 15, the State Water Project Delta pumps will shift from pumping 1,600 cubic feet per second (cfs) to 800 cfs. The ramp-down will be adjusted within 48 hours if turbidity clears beyond a certain threshold. Under the previous 2019 framework, the water supply loss of this action would have been 13,200 acre-feet – more than twice as great. (Additional information about Central Valley Project operations.)  

Bottom Line: Operating under a new federal framework that balances water supply and endangered species protection, the State Water Project is adjusting Delta operations for at least the next two days, depending upon conditions. A cutback in pumping under these conditions would have been required under both the 2019 and 2024 species-protection frameworks, but the 2024 rules are more finetuned to Delta conditions and give water project operators the ability to preserve more water supply while protecting Delta smelt. 

Source: CA. DWR