The Yakima River is a tributary of the Columbia River in south central and eastern Washington state, named for the indigenous Yakama people. The length of the river from headwaters to mouth is 214 miles. It is the longest river entirely in Washington state
The Yakima River and its tributaries have been heavily altered for the purpose of irrigated agriculture. There are numerous dams and irrigation canals. Irrigation runoff is in places returned to the river through canal drains. The irrigation system in the Yakima's watershed causes periods of both severe river dewatering and elevated flows, relative to the historic streamflow regime. As a result, discharge statistics for the Yakima River are heavily affected by the irrigation system. The USGS operates four streamflow gauges on the Yakima River.