The Clutha River / Mata-Au is the second longest river in New Zealand flowing south-southeast 338 kilometres through Central and South Otago from Lake Wanaka in the Southern Alps to the Pacific Ocean, 75 kilometres south west of Dunedin. It is the highest volume river in New Zealand, and the swiftest, with a catchment of 21,960 square kilometres, discharging a mean flow of 614 cubic metres per second.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.The ultimate source of the river is at the head of the Makarora River, close to the saddle of the Haast Pass, which flows into the northern end of Lake Wanaka. The southern end of the lake drains into the nascent Clutha close to Albert Town, where it is met by its first main tributary, the Hāwea River the outflow of Lake Wanaka's twin, Lake Hāwea. It is also met here by the Cardrona River.From here the river flows swiftly through the Upper Clutha Valley between ancient glacial terraces, negotiating a long section called the 'Snake' before reaching a rare switchback feature called the Devil's Nook near the town of Luggate. The river soon narrows as it passes through the Maori Gorge at Queensberry. Shortly thereafter it is joined by another tributary, the Lindis, before widening as it enters Lake Dunstan, an artificial lake created behind the massive hydroelectric dam at Clyde.Fifty kilometres south of Lake Wanaka, the Clutha reaches the town of Cromwell, which was substantially altered when the Clyde Dam project was commissioned in 1992. Here the river is joined by the waters of the Kawarau, which flows from Lake Wakatipu. Prior to the construction of the Clyde Dam, this river junction, known as the Cromwell Junction,was renowned for the difference in colour between the two rivers’ waters.The river then flows southeast through the inundated Cromwell Gorge to Clyde, and nearby Alexandra, where it is joined by the waters of the Manuherikia River. South of Alexandra the river widens again to form Lake Roxburgh, another artificial lake, behind the Roxburgh Dam, which was commissioned in 1956. The hydro reservoir flooded the Roxburgh Gorge and several large rapids including the Molyneux Falls and the Golden Falls. The town of Roxburgh sits close to the river, 120 kilometres downstream from Lake Wanaka.From here the river continues southeast past the towns of Ettrick, Millers Flat, and Beaumont, before flowing through the Rongahere Gorge admired for its native bush corridor and for the Birch Island native reserve. Beyond here, the river is met by the Tuapeka River at Tuapeka Mouth. At this point the river turns southward, before being met by its last major tributary, the Pomahaka River, which joins the Clutha 30 kilometres from the coast. The river passes the town of Balclutha before widening into the Clutha delta which contains the large flat island of Inch Clutha. Here the river divides into two branches, the Matau, which flows past Kaitangata, and Koau. Both branches flow into the Pacific Ocean at Molyneux Bay.The Clutha's average discharge is estimated at 614 cubic metres per second ,comparable to many much larger rivers. This heavy flow, combined with the relatively small size of the river in global terms, makes the Clutha notoriously fast-flowing, and it is often listed as one of the world's most swiftly flowing rivers, alongside Australia's Macleay and Fitzroy Rivers, the Amazon and Atrato Rivers in South America, and the Teesta River in the Himalaya.The waters of the Upper Clutha are clear turquoise, the result of glacial and snow-melt filtering when the water flows through Lake Wanaka. This is a rare characteristic for a high volume river. Below Cromwell, where the silt-laden Kawarau enters, the waters are less turquoise.