What US state is home to the man-made Fort Peck Lake?

Fort Peck Lake, or Lake Fort Peck, is a major reservoir in Montana, formed by the Fort Peck Dam on the Missouri River. The lake lies in the eastern prairie region of Montana approximately 140 miles (230 km) east of Great Falls and 120 miles (190 km) north of Billings, reaching into portions of six counties.

With a volume of 18,700,000 acre feet (23.1 km3) when full, Fort Peck is the fifth largest artificial lake in the United States. It extends 134 miles (216 km) through central Montana, and its twisting, inlet-studded shoreline has a total length of some 1,520 miles (2,450 km). The lake covers an area of 245,000 acres (99,000 ha), making it the largest in Montana by surface area, although Flathead Lake has a larger volume due to its greater depth.

The dam and reservoir were built to enhance navigation on the Missouri River, and supply enough water to provide a 9-foot deep channel from Sioux City, Iowa, to the mouth of the Missouri just above St. Louis. Fort Peck Dam was built from 1933 to 1940 by the U.S. Army Corps of Engineers; water impoundment began in 1937 and the reservoir was first filled to capacity in 1947. The reservoir is also a tourist attraction, with 27 designated recreational sites bordering its shores.