Lower Willamette

Watershed Hydrology

The Lower Willamette Watershed, located in western Oregon, covers an area of approximately 2,500 square miles. It is mostly characterized by a Mediterranean climate with mild, wet winters and dry summers. The watershed receives an average annual precipitation of 36 inches, and the majority of it drains into the Willamette River. The snowpack in the watershed typically ranges from 0-60 inches, with the highest amounts occurring in the higher elevations. The surface water quality in the watershed is generally good, but there are occasional concerns with high temperature and sediment levels. The watershed includes several large reservoirs, such as the Detroit Reservoir and the Big Cliff Reservoir, that are used for water supply and recreation. In recent years, the watershed has experienced drought conditions due to a lack of snowpack and below-average precipitation.


Surface Flows

Lower Willamette Watershed

Snowpack Depths

Lower Willamette Watershed

Dams & Reservoirs

Lower Willamette Watershed

Groundwater Levels

Lower Willamette Watershed

Lower Willamette Rivers

Rivers of the Watershed