Coldwater Lake

As a result of the collapse of the north face of Mount St. Helens on May 18, 1980, a debris avalanche blocked the flow of Coldwater Creek, which formed Coldwater Lake. Coldwater Lake would have overtopped the blockage in late 1981 or early 1982, which probably would have resulted in serious flooding downstream. Therefore, a spillway was constructed in 1981 to stabilize the lake level and prevent an uncontrolled breach. Lake level monitoring stopped following the 1998 water year because the lake blockage was considered stable and catastrophic breakout was determined to no longer be a significant threat.