Current Water Supply Levels

    Water Supply Conditions at Lake Sonoma, Lake Mendocino

    The Sonoma County Water Agency manages the water supply storage within Lake Mendocino and Lake Sonoma.  The U.S. Army Corps of Engineers operates the flood control storage of each reservoir.  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 provides a majority of the Water Agency's service area with its drinking water. Learn more about current drought conditions here.

    Please note: these visual charts are updated weekly. Click here to view water supply data tables updated daily.

    Water Storage Graph

    *Note each day after March 1, the Water Supply Pool in Lake Mendocino is allowed to encroach into the Flood Control Pool, thus resulting in changing Water Supply and Flood Control pool numbers. The Target Water Supply Storage Curve represents modeled daily average storage of Lake Mendocino for periods of Normal water supply conditions as determined by the Russian River System Hydrologic Index and Dry Spring 1 conditions as determined by combined Lake Pillsbury and Lake Mendocino storage on June 1.  The criteria for these conditions is defined in the State Water Resources Control Board Decision 1610.

    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 when the lake levels are in the water supply pools. The US 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.

    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.


    Current Reservoir, Russian River, and Water Transmission System Data

    View in-depth data tables for Lake Mendocino, Lake Sonoma, the Russian River, and the Water Transmission System.


    Rainfall Data

    Current Water Year vs. Average For This Date


    2014-10-01 - 2015-09-28
    2014-10-01 - 2015-09-28

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