Wiktionary
n. A crescent-shaped lake formed near a flat-valleyed river when one of its meanders becomes pinched off and isolated.
WordNet
n. a crescent-shaped lake (often temporary) that is formed when a meander of a river is cut off from the main channel
Wikipedia
Oxbow Lake, located in Saint Paul, Virginia, offers the Saint Paul community a recreational area with walking and biking paths, a fishing area, and a picnic area. Saint Paul High School also uses its mile-round path to hold cross-country meets throughout the season.
Usage examples of "oxbow lake".
Of more importance is that a former channel may indicate the river's course has changed-which would produce the oxbow lake your father spoke of.
The pond was the nearest possible thing to an oxbow lake, still connected to the stream but without the rushing waters.
Already the water level of the Falche where the Fal and the Chean met was two-thirds of what the older armsmen said was normal, and, based on the shape of the banks and the traces of old river beaches and the dried-up oxbow lake to the northwest of Falcor, they seemed to be right.
The distance is almost double that from the Horn at the Channel Mountains to Oxbow Lake along the tundra.