Soap Lake is a meromictic lake in the town of Soap Lake, Washington formed by the Missoula Floods at the foot of the Grand Coulee. The lake gets its name from the naturally occurring foam that gives its water a soapy appearance and because the lake's mineral-rich waters have a slick, soapy feel. The lake is approximately 2 mi.² (5.12 km²) in area and 70 feet (21.2 m) deep. Nearly twenty thousand years ago, as glaciers moved south, one ice sheet plugged the Clark Fork of the Columbia River, which kept water from being drained from Montana. Consequently, a significant portion of western Montana flooded, forming the gigantic Lake Missoula. Eventually, enough pressure accumulated on the ice dam that it gave way. It is generally accepted that this process of ice-damming of the Clark Fork, refilling of Lake Missoula and subsequent cataclysmic flooding happened dozens of times over the years of the last Ice Age. This sudden release put parts of Idaho, Washington, and Oregon under hundreds of feet of water in just a few days. These extraordinary floods created the Grand Coulee and Dry Falls in a short period. Similar glacial flooding on a smaller scale kept the falls flowing for several thousand years. Once the ice sheets that obstructed the Columbia melted, the river returned to its normal course leaving the Grand Coulee and the falls desiccated. Today, this massive cliff can be viewed from the Dry Falls Interpretive Center, part of Sun Lakes State Park, and located on Route 17 near the town of Coulee City. Admission is free. | 
