Mangatangi River facts for kids

The Mangatangi River is a waterway in New Zealand. It starts on the eastern side of the Hunua Ranges. The river flows generally south. It joins the Ruaotehuia Stream near State Highway 2. After this, it becomes the Maramarua River.

The name Mangatangi can mean a few things. It might mean "stream of weeping." It could also mean "rippling stream" or "babbling brook."

Neighbouring areas

		Hunua Ranges
	Hunua		Firth of Thames
		Mangatangi River
	Mercer	SH2

Is it a River or a Stream?

Sometimes, the Mangatangi is called a "stream." Other times, it's called a "river." A river is usually a large natural stream. The New Zealand Geographic Board has not yet given it an official name.

Maps often show it as a "Stream." However, some groups like LAWA call it a "River." The Regional Council also uses "River" in some documents. But in other plans, they call it a "Stream." Old records from the 1890s also called it a "River."

How the River Was Formed

The Mangatangi River begins as many small streams. These streams flow down the eastern slopes of the Hunua Ranges. The ground here is made of hard rocks. These rocks are called greywacke and argillite.

The river flows over these ancient rocks. A large crack in the earth, called the Mangatangi Fault, runs beside the river. In its upper parts, the river is usually shallow. It flows quickly over small stones and gravel.

How People Use the River

The Mangatangi River is important for many reasons. People use it for water and for fun activities. In the past, it was also used for transport.

The river also provides gravel. This gravel is used to build and fix local roads. Long ago, there was also a flax industry here. Flax is a plant used to make ropes and fabrics.

Mangatangi Dam

A large earth-fill dam was built on the river. It was built between 1972 and 1977. The dam is 78 m (256 ft) high and 340 m (1,120 ft) wide. It can hold a huge amount of water. This water covers an area of 169 ha (420 acres). The dam has a special overflow system. It is called a bellmouth spillway.

Bridges Over the River

Several bridges have been built over the Mangatangi River. In 1897, a wooden bridge was built. By 1914, it needed repairs. A flood washed away a temporary bridge in 1922. A new one was being built at that time.

Further upstream, another bridge called Stubbs Bridge was built in 1922. It was also washed away by a flood in 1966. A new Stubbs Bridge was built in 1967. A larger bridge with concrete supports was opened in 1924.

River Life: Plants and Animals

Animal Species in the River

Many types of fish live in the Mangatangi River. Some fish, like rainbow and brown trout, were brought here by people. Other fish, like koi carp and mosquitofish, are now considered pests. They can harm the native fish. Trout were first put into the river in 1885.

The water quality is good near the start of the river. But it gets worse further downstream. This is because of farming nearby. Near the Watercare Services measuring station, only eels and Crans bully were found. Galaxiids, another type of native fish, are mostly not found upstream of this point. Longfinned and shortfinned eels are common. In the past, people tried to catch eels. They thought eels were harming other fish.

Different types of ducks can be seen on the dam's reservoir. These include Grey teal, brown teal, and grey duck.

Environmental Challenges

Measurements show that the river's water quality is not always good. Near its mouth, it is among the worst 25% of waterways in New Zealand for many pollutants. The land around the river is mostly fertile farmland. This means there is a lot of agriculture.

Pollution from farms can get into the river. This happens when chemicals or animal waste leach into the ground. It also happens when rainwater runoff carries pollutants into the river.

Removing native plants from the land has also caused problems. It has led to more soil washing into the river. This makes the river silty. In the past, logs were floated down the river. This also made the river silty.

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