Here is a drone view of the Historic Bidwell Bar Bridge and Lake Oroville in Butte County. Lake Oroville storage is now up to 86 percent of capacity and 121 percent of historical average for this time of year, according to the California Department of Water Resources. Photo courtesy of California Department of Water Resources

 

NORTHERN CALIFORNIA (MPG) – On March 25, the Department of Water Resources (DWR) announced that wet and cold storms in March have allowed for another increase to the State Water Project (SWP) allocation forecast for 2025.

The allocation has increased to 40 percent of requested water supplies, up from 35 percent last month. The State Water Project provides water to 27 million Californians and 750,000 acres of farmland.

The latest allocation forecast is based on increases in precipitation, snowpack and reservoir storage in the past month. The allocation increase comes ahead of the April 1 snow surveys next week, when Sierra Nevada snowpack typically peaks.

“As we near the end of the wet season, our focus shifts to snowpack runoff and whether temperatures allow for a slow melt so we can capture as much of that runoff as possible,” said Department of Water Resources Director Karla Nemeth. “Despite periods of extremely dry conditions this season, water managers have been able to effectively capture, move and store water for use later this year while also maintaining flood protection.”

The State Water Project was able to increase storage this month at its largest reservoir, Lake Oroville, and nearly fill the State Water Project’s share of storage at San Luis Reservoir in Merced County. That storage will help meet the needs of State Water Project contractors and their customers this year as well as provide some water supply next year if dry conditions return. 

Lake Oroville storage is now up to 86 percent of capacity and 121 percent of historical average for this time of year. Department of Water Resources has been releasing water from Lake Oroville to maintain enough empty space in the reservoir for flood management. As spring progresses, the need for flood space will diminish and storage could increase.

In the Sacramento-San Joaquin Delta, April and May are ecologically important times and the State Water Project will need to adjust operations accordingly. Pumping rates will likely fall to minimum levels during those months to protect endangered fish species. Releases from Lake Oroville for endangered species and water quality protection also might be necessary, depending upon precipitation and other factors.

These constraints reinforce the need for California to invest in additional water supply infrastructure to provide operational flexibility. The proposed Sites Reservoir and Delta Conveyance Project would have been hugely beneficial to water supply had they been in place this season. The Delta Conveyance Project could have captured more than 750,000 acre-feet of additional water supply this winter, which would have translated to a 20-percent increase in the current State Water Project allocation, on top of the increase announced on March 25.

Each year, Department of Water Resources provides State Water Project allocation forecasts based on available water storage, projected water supply and water demands. Allocations are updated monthly as snowpack, rainfall and runoff information is assessed, with a final allocation typically determined in May or June. Any additional increases in the 2025 State Water Project allocation will depend heavily on the water content and runoff of the Sierra Nevada snowpack.

Learn more about how the State Water Project allocation process works at water.ca.gov/News/Blog/2025/Jan-25/Get-the-Facts-About-the-State-Water-Project-Allocation.

The allocation forecast notice to State Water Contractors and historical data on State Water Project allocations are available at water.ca.gov/programs/state-water-project/management/swp-water-contractors.