Formation
When meander bends become giant loops, there is a thin piece of land left between the beginning and the end of the meander. This is the meander neck.

As the river neck becomes very narrow, the river can break through. For a short time, water flows both round the meander (which is now called a backwater) and across the meander neck.

Eventually the river cuts off the backwater completely and flows across what used to be the meander neck. For a short time, an oxbow lake is left behind. It is called an oxbow lake because it is shaped like the old fashioned 'U' shaped yoke that was once used to hitch an ox to a plough. The oxbow lake lasts until it becomes overgrown with weeds and filled in with soil. This happens quite quickly as it is cut off from the main river and therefore doesn't get any water.