The River Axe is a river in Dorset, Somerset and Devon, in the south-west of England. It rises near Beaminster in Dorset, flows west then south by Axminster and joins the English Channel at Axmouth near Seaton in Lyme Bay. During its 22-mile (35 km) course it is fed by various streams and by the tributary rivers Yarty and Coly.
It is a shallow, non-navigable river, although its mouth at Axmouth has some boating activity.
The name derives from a Common Brittonic word meaning "abounding in fish", which is also the root for the River Axe in the Bristol Channel as well as the Exe, Esk, Usk and other variants. The name is cognate with (plural of ), the Welsh word for fish.
In 1999, a section of the river extending for 13 kilometres (8.1 mi)—from the confluence with the Blackwater River (ST325023) to Colyford Bridge (SY259927)—was designated a Site of Special Scientific Interest (SSSI). It was described as supporting "an exceptionally diverse aquatic and marginal flora". The river's diversity comes from its active geomorphology, which has created a number of natural features that support niche ecologies; it also comes from there being a limited number of trees on the river bank, allowing in light; and also the riverbed stability in the lower reaches of the river. A majority of the SSSI runs through Devon; only 150 metres runs through Dorset. The underlying geology of the riverbed is alluvium with areas of valley gravel, clay, shale and marl. The fish life in the river is considered of European interest; aquatic life more generally includes salmon, bullheads, otters, medicinal leeches and kingfishers; all are of particular value, as is the diverse aquatic and marginal plant life. The geomorphology of the meanders south of Axminster are the particular geological interest.