The Clutha River / Mata-Au is the second longest river in New Zealand and the longest in the South Island. It flows south-southeast through Central and South Otago from Lake Wanaka in the Southern Alps to the Pacific Ocean, south west of Dunedin. It is the highest volume river in New Zealand, and the swiftest, with a catchment of , discharging a mean flow of . The Clutha River is known for its scenery, gold-rush history, and swift turquoise waters. A river conservation group, the Clutha Mata-Au River Parkway Group, is working to establish a regional river parkway, with a trail, along the entire river corridor. The name of the river was changed to a dual name by the Ngai Tahu Claims Settlement Act 1998.