The Yakima River Basin consists of approximately located in south central Washington State. It is bounded by the Cascade Mountains on the west, the Wenatchee Mountains on the north, Rattlesnake Mountain and the Rattlesnake Hills on the east, and the Horse Heaven Hills to the south. The basin encompasses areas designated by the Washington Department of Ecology as the Upper Yakima Water Resource Inventory Areas (WRIAs) 38 and 39 and the Lower Yakima WRIA 37. The dividing line between these northern and southern sections is the confluence of the Naches and Yakima Rivers.