Lake Oahe Lake Oahe Lake Oahe (oh-WAH'-hee) is a large reservoir behind Oahe Dam on the Missouri River; it begins in central South Dakota and continues north into North Dakota in the United States. The lake has an area of and a maximum depth of . By volume, it is the fourth-largest reservoir in the US. Lake Oahe has a length of approximately and has a shoreline of . 51 recreation areas are located along Lake Oahe, and 1.5 million people visit the reservoir every year. The lake is named for the 1874 Oahe Indian Mission. Lake Oahe begins just north of
Perunchani Dam of the reservoir. The dam is located about from Nagercoil, the administrative headquarters-town of Kanyakumari District, and about from the town of Kulasekharam. The average annual rainfall in the catchment is , and the average annual yield at the dam site is . The dam was constructed between 1948–1953 by the then State of Travancore-Cochin. The height of the straight gravity masonry dam above the deepest foundation is , with Full Reservoir Level (FRL) at , which is also the Maximum Water Level (MWL). The dam is long. The gross storage capacity of the reservoir is at the FRL, which