Potholes are holes in the river bed. They vary in size from a few centimetres to several metres in diamter.
Potholes are formed by corrasion. Pebbles carried by the river are swirled around on the river bed. This action erodes the rock on the river bed forming potholes. Over time, they may widen and join with other potholes to form larger potholes, and the whole river bed is deepened.