Soap Lake is a meromictic soda 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 square miles (5.2 km2) in area and 70 feet (21 m) deep.

Grant County is a county located in the U.S. state of Washington. As of the 2020 census, the population was 99,123. The county seat is Ephrata, and the largest city is Moses Lake. The county was formed out of Douglas County in February 1909 and is named for U.S. President Ulysses S. Grant.