Oxbow lakes are formed when the neck of a looping meander is broken through (A), usually during times of flood. The entrances to the bypassed meander are soon blocked by silt (B).
An oxbow lake is a crescent-shaped section of a river channel that no longer carries the main discharge of water. An oxbow lake forms from a meander. As sediment is deposited, the meander becomes cut off from the river to create a lake. Once formed, the lake gradually shrinks as silt fills it in; vegetation grows on the new muddy area, and the land can be reclaimed. The name derives from the shape of the lake, said to resemble an ox's collar.