From Wikipedia, the free encyclopedia::
An oxbow lake is a U-shaped lake water body formed when a wide meander from the mainstem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape that results from this process. In Australia, an oxbow lake is called a billabong. By itself, the word oxbow can also mean a U-shaped bend in a river or stream, whether or not it is cut off from the mainstream.
this is a pretty interesting phenomenon ron brought to my attention yesterday, and a few resources to further your understanding of it. did you guys get a chance to visit chamizal national memorial? at this site there are a couple of videos describing the surrounding political issues now and historically regarding a "living boundary" such as el rio. these short videos describe the disputes over territories as the river meandered over time, and chamizal to memorialize the resolution of some disputes between the us and mexico - a joint effort in ultimately physically MOVING the river. http://www.nps.gov/cham/historyculture/chamizal-history.htm