Water Resource Inventory Area 32 (WRIA 32) or the Walla Walla Basin includes parts of five counties in Washington and Oregon; Walla Walla and Columbia Counties in Washington and Umatilla, Union and Wallowa Counties in Oregon. Occupying an area of 4,553 square kilometers (1,758 square miles) the WRIA's main river is the Walla Walla River and its tributaries originate in the Blue Mountains of southeastern Washington and northeastern Oregon and flow north and west to enter the Columbia River at Lake Wallula behind McNary Dam. About 73 percent of the drainage lies in Washington. Elevations in the subbasin range from about 1,800 meters at mountain crests to about 80 meters at the Columbia River. There are currently more than 30 species of fish inhabiting the Walla Walla Subbasin, 17 of which are native. The Basin is home to endangered Mid-Columbia Steelhead and Bull Trout; Chinook Salmon are also being reintroduced.