The Newton River is a river in Fiordland, New Zealand. It drains Lake Fraser south-westward into the Tasman Sea just south of West Cape. Newton River is an official name, gazetted on 4 February 1960, after being in use by local fishermen for some time. It is about 9 km long. The river flows over the Newton River pluton of Carbonferous biotite, granodiorite and granite, which has been glaciated and also forms a rock arch to the south of the river mouth, where a marine terrace has been uplifted within the last half a million years. The beech forest in the valley includes black beech (tawairauriki), kāmahi, and silver beech (tawhai).