Although the Missouri River generally is the boundary between Iowa and Nebraska, the river in 1877 had avulsed one of its bends, cutting off the land that later became the city of Carter Lake on the western side. The Supreme Court six years earlier had mentioned the circumstances of Carter Lake when it ruled on a boundary dispute between the two states in Nebraska v. Iowa, 406 U.S. 117 (1972).
The Missouri River's boundary between Iowa and Nebraska shifted in 1877, creating land that became Carter Lake on the western side. This event was previously addressed by the Supreme Court when it ruled on a boundary dispute between Iowa and Nebraska in the case of Nebraska v. Iowa, 406 U.S. 117 (1972).