The Umatilla River and its tributaries drain Oregon's northwestern corner of the Blue Mountains. The upper parts of the basin historically supported great runs of anandromous fish, but activities in the lower parts of the basin have dwindled those populations. Now, the McKay Reservoir and dam on McKay Creek are used to augment flow in the Umatilla River.
Flow is depleted by diversion into various irrigation canals.
Most of the flow in the lower parts of the Umatilla River is due to irrigation returns and groundwater recharge. The Oregon Department of Environmental Quality is working with the Umatilla Basin Watershed Council, the Confederated Tribes of the Umatilla Indian Reservation, and other agencies to develop a Total Maximum Daily Load for the river. The Umatilla River is listed as water quality limited for algae, fecal coliform, flow modification, pH, nutrients, and temperature. Water quality data were routinely collected by the DEQ Laboratory in water years 1986-1995 and intensive monitoring was conducted in the summer of 1993. Additional intensive monitoring was performed in 1996, however that data is not included in this report.