Oxbow lake

Oxbow lake in Slovakia

An oxbow lake is a lake, or area of water, in a U-shape. It is made by special bends in a river, called meanders, getting farther away from the river until they become separate. The river becomes straight and the bend becomes a lake. This happens due to floods or when a meander's neck gets too thin.

Why does this happen?

Water flows at different speeds at different parts of the river. In the middle, farthest away from the sides (or banks), the water flows fastest. At the banks, the water flows slowest. When the river bends, water flows faster on the outside of the bend than the inside. The fast water on the outside 'erodes' the outside of the bend. This means it breaks bits of the bank off. At the same time, the slow water on the inside of the bend leaves behind mud, sand and parts of plants (deposition). Together, these make the bend move in the direction of the outside of the bend.

The bend moves farther and farther along until it leaves the river. The river becomes straight and the bend is left as an oxbow lake.