Mount St Helens Eruption; Spirit Lake and Toutle River Watershed 

After the Mount St Helens 1980 eruption, the U.S. Army Corps of Engineers mobilized to address flooding and sediment concerns at Spirit Lake and newly created Castle and Coldwater lakes. The Gifford Pinchot National Forest is responsible for operating, maintaining and repairing the 1.6 mile Spirit Lake tunnel, and the engineered channels at Castle and Coldwater lakes.