The original name, Exe, is Brythonic, deriving from the Ancient British word *Iska meaning "fishes" or "fish-place" and cognate with the modern Welsh word Pysg (fishes).This derivation applies to many similarly named rivers throughout Britain including the Axe, Exe and Usk, with the names evolving local distinctions over the centuries.

The Beaulieu River rises near Lyndhurst in the centre of the New Forest, a zone where copses and scattered trees interrupt the relatively neutral sandy heath soil, however with insufficient organic uneroded deposition over millennia to prevent an upper charismatic dendritic drainage basin of many very small streams.

[2] Below, the tidal river (estuary) continues to flow south-east through the Forest, passing the hamlet of Bucklers Hard and entering the Solent at Needs Ore. For its final kilometre, it is separated from The Solent by a raised salt marsh known as Gull Island.

Bucklers Hard was once a significant shipbuilding centre, building many wooden sailing ships, both merchant and naval, including Nelson's Agamemnon.

There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish.