The Oreti (or New) River is one of the main rivers of Southland, New Zealand, and is 170 kilometres in length.

The Oreti has its headwaters close to the Mavora Lakes between Lake Te Anau and Lake Wakatipu, and flows south across the Southland Plains to its outflow into Foveaux Strait at the southeastern end of Oreti Beach. En route, it runs through the towns of Lumsden and Winton, before passing through the city of Invercargill, close to the river's estuary.

For the final part of the river's length, around the city of Invercargill and the river's estuary just south of the city, it is known as the New River, a name occasionally encountered to refer to the whole river.