Big Spirit Lake is a natural body of water, approximately 5,684 acres (2,300 ha) in area, in Dickinson County in northwest Iowa in the United States. It is part of the chain of lakes known as the Iowa Great Lakes, the northern shore of the lake straddles the border with Minnesota. It is the largest natural lake in Iowa. The Dakota name for the lake was Minnewaukon. Early French traders named it Lac d'Esprit after the Native legends of an evil spirit who dwelled in the lake.

Its maximum depth is 24 feet (7.3 m), and the mean depth is 17 feet (5 m). The drainage area of the lake is approximately 22 square miles (57 km²). It has a drainage area of approximately 75 mi² (194 km²), most of which is in Minnesota.

Geologically, the lake, like its neighbors, is a glacial pothole, a remnant of the most recent ice age approximately 13,000 years ago.

The lake is a popular fishing destination in the region. It contains over 40 species of fish, 13 of which are typically caught. Fishing for walleye and yellow perch is typically done by boat or through the ice. Fishing for bullhead is common from the shore during the spring. A state-operated fish hatchery also provides significant populations of largemouth bass, smallmouth bass, northern pike, muskie, crappie, and bluegill.

The Iowa all-time big fish records for freshwater drum and muskellunge were set from catches in the lake.

Kiteboarding is also a popular activity on Big Spirit Lake.

• East Okoboji Lake
• West Okoboji Lake

• Iowa Department of Natural Resources site on Spirit Lake
• University of Iowa site on Spirit Lake chemistry
• Spirit Lake Fish Hatchery Documentary produced by Iowa Public Television
• Spirit Lake, Where Ice Fishing is Hot Documentary produced by Iowa Public Television