The River Marden is a small tributary of the River Avon in England. It flows from the hills surrounding Calne and meets the Avon about a mile upstream of Chippenham. The river has a mean flow of 43 cubic feet per second (1.2 m3/s).

The River Avon is a river in the southwest of England. To distinguish it from a number of other rivers of the same name, it is often called the Bristol Avon. The name 'Avon' is loaned from an ancestor of the Welsh word afon, meaning 'river'.