An oxbow lake, also called a horseshoe lake, is a crescent of still water in an abandoned loop of river channel, named for the curved piece of wood used to yoke oxen. An oxbow forms when a river cuts across the neck of a meander and shortens its course. The former channel then ﬁlls with river overﬂow or groundwater seepage to form the oxbow. Having no current and no outlet, the lake is doomed. Gradually it ﬁlls with silt and decaying vegetation. Marsh plants and swamp trees encroach its edges. In time, the open water disappears, and only a swale, known as a meander scar, is left behind. Oxbows are so common in the landscape that the Geographic Names Information System of the U.S. Geological Survey lists 169 place-names in the United States containing the word oxbow. Given the transitory nature of the landform, possibly a minority of the namesakes of those places still exist as lakes.