Current Water Supply Levels

Rainfall, Weather, and Streamflow Data

January 9, 2023 - The series of recent storms has resulted in substantial increased pool elevations at Lakes Mendocino and Sonoma and unfortunately flooding on the Russian River. The U.S. Army Corps of Engineers San Francisco District’s current plan is to continue to hold back water during the remaining series of storms this week. Both dams and the lakes they impound combine to regulate just 18% of the Russian River watershed. They function to restrict additional water from entering the river during periods of high flows, to allow for a managed flood control release to the river after the threat to downstream communities recedes. The reservoirs are recovering after reaching historically low levels. Given the anticipated additional rain forecast for this week, the District anticipates the likelihood for flood control release would occur at Lake Mendocino no earlier than Thursday January 12, 2023, while no flood control releases at Lake Sonoma are anticipated in the next week. The current outlook, and any changes due to updated forecasts, will continue to be coordinated with Sonoma Water, City of Ukiah, and other partners and communities downstream of our lakes.

For information on Flood Forecasts & Emergencies, see here.

Sonoma Water OneRainLake MendocinoLake Sonoma

Weekly Water Supply Reservoir Levels for Lake Sonoma, Lake Mendocino, and Lake Pillsbury

*Note that between March 1 and September 30 in Lake Mendocino, the Water Supply Pool is allowed to encroach into the Flood Control Pool and transitions to a higher operational level for the summer season. The "Target Water Supply Curve" represents the normal daily storage level for each day of the year. The daily storage levels were determined based on reservoir modeling of an average year under “Normal” water supply conditions as designated by the Russian River System hydrologic index. Categories of water supply conditions are based on criteria defined in the State Water Resources Control Board Decision 1610. These conditions establish the applicable instream flow requirements.

Our region is still in Drought

For information on the 2022 Drought, see here.

About Lake Sonoma and Lake Mendocino

Sonoma Water is the local cost-sharing partner for Lake Mendocino and Lake Sonoma, and determines the amount of water to be released from each reservoir when the lake levels are in the water supply pools. The U.S. Army Corps of Engineers determines the amount of water to be released when the lake levels are above the water supply pools and in the flood control pools.

Lake Mendocino relies on year-to-year rainfall to fill as well as water diverted from the Potter Valley Project. Lake Mendocino is a key drinking water source for the cities of Ukiah, Healdsburg, Cloverdale and Hopland, and also provides water to Sonoma Water’s Russian River water supply system. Water releases from Lake Mendocino support flows in the Russian River for the threatened Chinook salmon and steelhead trout during the fall and winter seasons. 

Lake Sonoma is about four times larger than Lake Mendocino and can provide multiple years of water supply. Lake Sonoma relies on rainfall to fill and supports a dynamic and fragile ecosystem in Dry Creek that includes the endangered coho salmon and threatened steelhead trout. Lake Sonoma provides a majority of Sonoma Water's service area with its drinking water.

The Russian River is a managed river system with reservoir releases controlling river flows, especially throughout most of the summer and fall. When tributary stream flows are low, Sonoma Water releases water stored in the reservoirs to supplement the natural flows in the Russian River to provide adequate flows for water supply, recreation and aquatic habitat. A release from a reservoir can be categorized as being of ‘pass-through water’ or ‘stored water’. The term ‘project water’ is often used instead of stored water and is used to describe water that is present because of the dam and reservoir project. Pass-through water is water flowing into the reservoir that is not stored in, but passes through, the reservoir. Project water releases to supplement the natural flows in the Russian River and Dry Creek are necessary to meet mandatory minimum streamflow requirements that exist for both of these watercourses.