Reclamation announces Yakima basin water supply—May forecast

Media Contact: Annette Ross, (208) 378-5322,

For Release: May 07, 2020

YAKIMA, Wash. – The Bureau of Reclamation’s May 2020 Total Water Supply Available (TWSA) forecast for the Yakima basin indicates the water supply will fully satisfy senior water rights, while the junior water rights will be limited to an estimated 91% of their full entitlements this irrigation season.

“March and April were very dry throughout the basin, with only 45% of average system precipitation, the fourth lowest in the 109 years of record,” said Chuck Garner, Yakima Project River Operations supervisor. “The Yakima basin reservoir storage is 72% full, which is 98% of average. The snowpack is 76% of average.”

Reclamation manages the water in the five Yakima Project storage reservoirs, along with the basin’s unregulated inflows to fulfill water rights, water contracts and instream flow obligations. Water shortages in the basin are shared equally by the junior water rights, which represent over half of the water rights in the basin.

Specific water-delivery levels, such as water rights allocations and streamflow targets, will be set, normally in June, when the Yakima system requires reservoir storage releases to meet irrigation diversions and river flows. Reclamation will provide an updated water supply forecast and water allocation each month—at least through July—using the latest data to reflect changing conditions as they develop.

The May forecast is based on flows, precipitation, snowpack and reservoir storage as of May 1, along with estimates of future precipitation and river flows. Other future weather conditions that determine the timing of the runoff and the demand for water also are critical in determining streamflows, prorations and the extent to which the reservoirs fill.

“Our forecasts assume close to normal conditions going forward. When it is this dry in the spring, the water supply will drop,” says Garner. “We are grateful that, despite the dry conditions, the snow and reservoir storage appear adequate to meet normal demands, but we must manage the water carefully.”

For more information, visit Reclamation’s website at

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The Bureau of Reclamation is a federal agency under the U.S. Department of the Interior and is the nation's largest wholesale water supplier and second largest producer of hydroelectric power. Our facilities also provide substantial flood control, recreation opportunities, and environmental benefits. Visit our website at and follow us on Twitter @USBR.

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