Current Water Supply Levels

    Water Supply Conditions for Lake Sonoma, Lake Mendocino

    Please note: the charts below are updated weekly. View daily updated reservoir levels and Russian River flow data here.

    Water Storage Graph

    *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 Storage 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.

    On 12/16/16, The Water Agency submitted a Temporary Deviation to the Water Control Manual, to request the Army Corps of Engineers allow an additional 5,825 Acre Feet of water to be stored in the Flood Control Pool for Lake Mendocino. Learn more about reservoir operations.

    Rainfall Data

    Current Water Year vs. Average For This Date. The Water Year begins on October 1.

    2017-10-01 - 2018-09-16
    2017-10-01 - 2018-09-16

    View the National Weather Service's long-term weather forecast for Ukiah and Lake Mendocino.

    About Lake Sonoma and Lake Mendocino

    The Sonoma County Water Agency (Water Agency) 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.  Learn more about how the Water Agency is working with the Corps to store more water in Lake Mendocino.

    Lake Mendocino relies on year-to-year rainfall to fill and 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 the Water Agency’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 the Water Agency'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, the Water Agency 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.