An ox- bow lake is formed from a river with meanders- if the student does not understand meanders I will cover this first.The meanders bend so much from high levels of erosion on the outside of the bend and deposition on the inside of the bend.Eventually the two outside bends end up next to each other form high erosion and then the water breaks through the meander forming a new straight channel.The old bend of the meander is left behind in a horseshoe shape lake which later dries up.The ox bow lake has been formed.