Lake Chouteau was a glacial lake in the late Pleistocene along the Teton River in present-day Teton County, Montana. It formed when the Laurentide Ice Sheet blocked regional drainage, trapping meltwater between the Rocky Mountains and the ice front. As the ice retreated, the lake drained eastward toward the Judith and Missouri rivers. It belonged to a broader system of temporary lakes on Montana’s western plains created when ice lobes blocked north- and east-flowing rivers. Geological evidence in the Teton basin, including scattered limestone boulders, cobbles, paleosols, till, and outwash, points to earlier glacial episodes, and the lake is known today only through that reconstructed geological record.