Department of
Environmental Quality

Subbasin at a Glance

Overview

The Wildhorse River watershed is part of the Brownlee Reservoir Subbasin, which is located in southwestern Idaho on the border between Idaho and Oregon.

The headwaters of the Wildhorse River originate in forested land at the southern end of the Seven Devils Mountains, which form the eastern border of Hells Canyon. The river flows southwesterly out of these mountains and enters the Snake River between Brownlee Dam and Oxbow Reservoir. This portion of the Snake River forms the border between the states of Idaho and Oregon. Although some of the southerly tributaries flow out of Washington County, the mainstem is located solely in the southern portion of Adams County. There are no towns and very few inhabitants located on the Wildhorse River. The unincorporated community of Bear is located in the Wildhorse Basin.

In 2000, the U.S. Environmental Protection Agency (EPA) added streams to Idaho's 1998 303(d) list of impaired waters that exceeded Idaho's temperature criteria. In the Brownlee Reservoir Subbasin, Wildhorse River was among those EPA additions.

In order to fully evaluate the heat loading to this river, its major tributaries (Bear Creek, Lick Creek, and Crooked River) were also examined.

Effective shade targets were established for Wildhorse River and its three major tributaries. An analysis of shade reveals that the Wildhorse River is slightly below target shade levels and would require a 12% reduction in its own solar load to achieve background conditions. Additionally, the heat loading in the river is compounded by the excess solar loading to Lick Creek, Bear Creek, and Crooked River. Most streams appear to be in relatively good condition and should be considered of relatively low priority for implementation.

Stream and Pollutant for Which TMDLs Were Developed

Wildhorse River

Temperature

Subbasin Documents

• Wildhorse River Subbasin Assessment and Total Maximum Daily Load (April 2007)
• Agriculture Implementation Plan (March 2010)
• Forestry Implementation Plan (February 2010)