15 Mile Creek, a tributary of the Columbia River, is actually 54 miles long. During the pioneer days, a road crossed the creek about fifteen miles up, hence the name. The headwaters are east of Mt. Hood, near Lookout Mountain. It drains approximately 370 square miles of the surrounding watershed which is 85% private land and 15% in the Mt. Hood National Forest.
Several species of anadromous fish inhabit the stream, including native runs of winter steelhead, Coho salmon, Chinook salmon, and Pacific and Western brook lamprey. Cutthroat and redband trout also inhabit the creek. The winter steelhead here are considered the easternmost population of any Columbia tributary. The Chinook that have been found in the watershed have only been documented in the since 1998. Whether they came from hatchery strays or native stock is unknown.
There are various limiting factors that exist on 15 Mile Creek. Much of the lower basin is primarily agricultural land utilized for crops and cattle. Reductions in stream flow, increased stream temperature, a lack of large woody debris, loss of side channels, channelization, and the reduction of healthy riparian areas are just a few of the results of these types of land use. There are also the obvious concerns of pesticide and herbicide runoff.