The river flow rates and water elevation in the Priest Rapids and Wanapum reservoirs are affected by a number of factors. They include: general river water conditions (low, medium or high water year depending on winter snow pack in the mountains), seasonal river flows, power demand, flows for fish protection, etc.
The Priest Rapids Project license allows a 6.5 ft. elevation variation of the reservoir at the Priest Rapids Dam (from 481.5 ft. above sea level to 488 ft.). At Wanapum Dam there can be 11.5 ft. elevation variation ( 560 ft. to 571.5 ft.). The reservoirs are usually operated in the upper range of those allowable river elevations.

The greatest fluctuations occur from mid October to late November in aid of salmon spawning down river from Priest Rapids Dam.
The greatest benefit to recreation use of the reservoirs comes from the Mid-Columbia Hourly Coordination Agreement. Begun in 1973, this agreement allows Grant County PUD Power Dispatchers to provide moment-by-moment coordination of the seven dams in the Mid-Columbia River area. The Power Dispatchers analyze the total electric requirements of the seven power plants and then allocate power generation to individual plants in a manner that results in less fluctuation of reservoirs at each dam.

The result is reservoirs operating at a higher average level and greater total power production. This has proven to be the most efficient means of operating the seven Mid-Columbia River dams.

Priest Rapids Reservoir Water Level Hourly Operation Data Report

Wanapum Reservoir Water Level Hourly Operation Data Report

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