Clean Water and Cold-Water Refuges are Important
The amount of water in streams in this region is characterized by extremes. Heavy rain and rain-on-snow events create peak water flows in the winter, and decreasing snowpack and glacial melt from the Olympic Mountains, as well as aquifer levels, affect flows in the summer. The river systems on the coast are less challenged by urban, industrial, or agricultural polluted runoff issues faced by other regions of Washington. One exception is the Chehalis River basin, a large and diverse, 2,700-square-mile watershed that is a microcosm of all western Washington watersheds combined.
Summer stream flows and temperatures are changing in this region, although in different ways along the northern and southern boundaries. Along the northern coast, rivers have less water but the water temperatures have remained hospitable to salmon, thanks to the rain and snowpack in the Olympic Mountains, groundwater supply, and few water withdrawals. In contrast, rivers in southwestern Washington have experienced both less water and warmer water in streams during the summer. Flows and temperatures in these rivers are influenced by precipitation as well as groundwater supply and water withdrawals.