Shellmouth Dam was built in 1968 to control flooding along the Assiniboine River. The dam measures 21 m (69 feet) in height and 1,218  m (3/4 mile) in length. Lake of the Prairies, which resulted from the construction of the dam, is 67 km (42 miles) long, and straddles the Manitoba-Saskatchewan border. The first 6 km (4 miles) of the lake is Asessippi Provincial Park’s central feature.