The Deschutes River begins in Lewis County and flows 57 miles from the Bald Hills to Capitol Lake, in Olympia. From the lake, a dam controls the discharge into Budd Inlet, draining a total of 126,609 acres of western Washington. Most of the precipitation falls in the winter and spring, from October through May – an average of 52 inches near Olympia and more than 90 inches in the upper watershed.
The river begins at an elevation of 3,500 feet amidst steep hills and high ridges. At the high points, snow accumulates and can cause flooding when it melts. In the mid-watershed, tributaries join the main river as the landscape becomes more level.
The lower part of the basin contains several aquifers, recharged primarily by rainfall. In late summer, many small streams are sustained by groundwater. In 1988, the USGS found that the Deschutes itself gained more than 44 percent of its flow between Rainier and Tumwater from groundwater seepage.
- Counties: Lewis, Thurston
- National Estuary Programs: Puget Sound
- Other Watersheds Upstream: None
- Other Watersheds Downstream: Puget Sound