Located in southwest Alaska, Lake Clark is a long narrow lake with a surface area of 128 square miles and an average depth of 324 feet. The lake occupies 4.3 percent of its 2,942 square mile basin. Most runoff to the lake occurs from June to September from six watersheds that range in size from 168 square miles to 1,157 square miles. The Tlikakila River has the largest inflow to the lake. Its basin is 622 square miles and glaciers cover about 36 percent of its area. Lake Clark mixes frequently and deeply. Temperature profiles indicate that Lake Clark stratifies only for a short period of time in July. The lake is fully oxygenated year-round, which helps to increase the productivity of the lake and partially explains the abundance of sockeye salmon. Primary productivity of Lake Clark appears to be limited by low light penetration resulting from turbid glacial inflows.