Lake Sammamish is a body of water in Washington state of the United States. Lake Sammamish lies to the east of Lake Washington and to the west of the Sammamish Plateau. The lake runs north to south, streching from the city of Issaquah, Washington in the south to Redmond, Washington in the north. Lake Sammamish is a freshwater body connected to Lake Washington via the Sammamish Slough, also called the Sammamish River. Issaquah Creek feeds the lake on the southern end.

Lake Sammamish and the surrounding area has been, in recent times, the most rapidly growing suburban district in the Greater Seattle Metropolitan Area. During the late 1990s and early 2000s, the cities of Redmond, Snoqualmie, Fall City, Issaquah and Bellevue have grown substantially. A new town, Sammamish, Washington was incorporated in 1999, because of the suburban growth.