The Mangatawhiri River is a river of the Auckland

Auckland Region

The Auckland Region was one of the sixteen regions of New Zealand, named for the city of Auckland, the country's largest urban area. With one third of the nation's residents, it was by far the biggest population and economy of any region of New Zealand, but the second-smallest land area.On 1...

 and Waikato Regions of New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

's North Island

North Island

The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...

. It flows generally southwest from its sources in the Hunua Hills southeast of Clevedon

Clevedon, New Zealand

Clevedon is a rural town in Auckland, New Zealand, located in the Franklin ward, one of the thirteen administrative divisions of Auckland city...

 before flowing through a system of irrigation canals at the northern edge of the Waikato Plains

Waikato Plains

The Waikato Plains are a large area of low-lying land in the northwest of the North Island of New Zealand. They are the floodplains of the Waikato River, the country's longest river....

 close to the town of Pokeno

Pokeno

Pokeno is a small town in New Zealand, located 50 kilometres southeast of Auckland. State Highway 1 originally ran through the town, but the upgrading of the highway in 1992 to expressway standards mean that the town has been bypassed....

. It reaches the Waikato River

Waikato River

The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...

 close to the township of Mercer.

The upper reaches of the Mangatawhiri are dammed to form reservoirs to store water for use by Auckland City.