The Grays Harbor watershed, located in western Washington state, covers an area of approximately 2,208 square miles. The watershed is characterized by its diverse hydrology, ranging from high-gradient mountain streams to lowland rivers and estuaries. The watershed receives significant precipitation throughout the year, with average annual precipitation ranging from 60 to 150 inches. In the winter months, snowpack can accumulate in the higher elevations, providing a vital source of water for the watershed during the dry summer months. Surface water quality in the watershed is impacted by agricultural runoff, logging practices, and urban development. The primary reservoir in the watershed is the Wynoochee Reservoir, which is used for hydropower generation and recreational activities. In recent years, the Grays Harbor watershed has experienced an increase in winter precipitation and a decrease in summer precipitation, which may be linked to changing climate conditions.