The Grey River / Māwheranui is located in the northwest of the

South Island The South Island ( , 'the waters of Pounamu, Greenstone') is the largest of the three major islands of New Zealand by surface area, the others being the smaller but more populous North Island and Stewart Island. It is bordered to the north by ...

of New Zealand. It rises 12 kilometres southwest of the

Lewis Pass Lewis Pass is the northernmost of the three main mountain passes through the Southern Alps in the South Island of New Zealand. With an elevation of 907 metres, it is slightly lower than Arthur's Pass and higher than Haast Pass. The pass is ...

in Lake Christabel, one of numerous small lakes on the western side of the

Southern Alps The Southern Alps (; officially Southern Alps / Kā Tiritiri o te Moana) are a mountain range extending along much of the length of New Zealand, New Zealand's South Island, reaching its greatest elevations near the range's western side. The n ...

, and runs westward for 120 kilometres before draining into the

Tasman Sea The Tasman Sea is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer Abel Janszoon Tasman, who in 1642 wa ...

Greymouth Greymouth () (Māori language, Māori: ''Māwhera'') is the largest town in the West Coast, New Zealand, West Coast List of regions in New Zealand, region in the South Island of New Zealand, and the seat of the Grey District Council. The populat ...

Thomas Brunner Thomas Brunner (April 1821 – 22 April 1874) was an English-born Surveying, surveyor and explorer remembered for his exploration of the West Coast, New Zealand, West Coast of New Zealand's South Island. Brunner was born in April 1821 in Oxfo ...

, who explored the area in the late 1840s, named the river in honour of

Sir George Grey Sir George Grey, KCB (14 April 1812 – 19 September 1898) was a British soldier, explorer, colonial administrator and writer. He served in a succession of governing positions: Governor of South Australia, twice Governor of New Zealand, Gov ...

, who first served as

Governor of New Zealand A governor is an administrative leader and head of a polity or political region, in some cases, such as governors-general, as the head of a state's official representative. Depending on the type of political region or polity, a ''governor'' ma ...

from 1845 to 1854. The

Ngāi Tahu Claims Settlement Act 1998 The Ngāi Tahu Claims Settlement Act 1998 is an act of parliament passed in New Zealand relating to Ngāi Tahu, the principal Māori (tribe) of the South Island. The act's purpose is to settle all of the tribe's claims under the Treaty of Wa ...

changed the official name of the river to Grey River / Māwheranui in 1998. The

Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...

name for the river system and surrounding area is ''Māwhera'', with ''Māwheranui'' being distinguished from the northern branch Little Grey River / Māwheraiti. The New Zealand

Ministry for Culture and Heritage The Ministry for Culture and Heritage (MCH; ) is the department of the New Zealand Government responsible for supporting the Creative New Zealand, arts, Culture of New Zealand, culture, New Zealand Historic Places Trust, built heritage, Sport Ne ...

gives a translation of "broad and widespread (river mouth)" for ''Māwheranui''. Numerous small rivers are tributaries of the Grey, and several of them also drain lakes. Notable among these are the

Ahaura River The Ahaura River is in the South Island of New Zealand. This river drains the western flanks of the Southern Alps and flows into the Grey River. The Ahaura and its many tributaries rise in the Lake Sumner State Forest park and enters the G ...

and the

Arnold River Arnold River may refer to: *Arnold River (Northern Territory), a tributary of the Hodgson River in Australia *Arnold River (New Zealand), a tributary of the Grey River *Arnold River (Saskatchewan), a tributary of the Rapid River (Cree River tributar ...

, the latter of which is the outflow of

Lake Brunner Lake Brunner ( or ) is the largest lake in the West Coast Region of New Zealand, located southeast of Greymouth. The main settlement, Moana, New Zealand, Moana, is on its northern shore. It is an important settlement and waystation for local M ...

, the largest lake of the northwest South Island. A small

hydroelectric Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...

station stands on the river 25 kilometres upstream from the mouth. The Grey River's mouth is protected by a large

sandbar In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or ...

, Greymouth bar, which is a notorious danger to shipping. Raw sewage discharges into the Grey River after heavy rainfall. Historically, sewage and stormwater from Greymouth, Cobden and Blaketown were discharged without treatment directly into the Grey River. Changes to the Grey District Council's wastewater schemes provide separation and treatment for sewage, except during periods of high rainfall, such as spring, when the capacity of the sewage treatment is exceeded.

References

{{DEFAULTSORT:Grey River Māwheranui Grey District Buller District Rivers of the West Coast Region Rivers of New Zealand