Fort Peck Dam, Montana

The Fort Peck Dam is the largest embankment dam in the USA, and the reservoir it holds back is the fifth largest in the USA. The dam is one of six major dams along the Missouri River, made by the Army Corps of Engineers, that completely transformed the upper Missouri, one of the longest and most important rivers in the nation. The dam was made by hydraulically pumping sediment from the river bottom into a pool that was raised as sediments settled, until it grew into the dam, six years later, which was then capped by rock. It was the largest hydraulically filled dam in the world when it was completed in 1940. As many as 11,000 people were working on it in 1936. It is more than a mile wide, and 250 feet tall. Fort Peck Lake, behind it, took years to fill, and its size varies, depending on runoff, but is generally 135 miles long, and has 1,500 miles of shoreline.