Moses Lake is a city in Grant County, Washington, United States. The population was 14,953 as of the 2000 census. According to the Washington State Office of Financial Management's April 1, 2008 estimate, the city has a population of 18,310. Major attractions include the Sand Dunes, Moses Lake,the Surf 'N Slide, the Ice skating rink and Baseball fields. Moses Lake is the largest city in Grant County.