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Wetlands of Ō Tū Wharekai

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Wetlands of Ō Tū Wharekai include kettle holes, ephemeral tarns, swamps and bogs, as well as the Ashburton Lakes and the Rangitata River.

Kettle Holes

A kettle hole is a bowl-shaped hollow in the loose rocks that have been left by a melting glacier. When a melting glacier moves back, large blocks of ice are left behind. These blocks of ice are covered in outwash. When the ice blocks melt, kettle holes are left behind.


Swamps get their water from streams, ground water or run-off.


Bogs get their water from rainwater. They are often found in alpine areas.

Ephemeral (temporary) tarns

  • small mountain lakes that are sometimes dry
  • the plants are called turf-vegetation and look like a thick carpet
  • they are used by water birds
  • they are often made by a kettle hole

The table below shows photos of the same ephemeral tarn. It is a good way of seeing how the tarn changes during the year.




early May

mid May

late May




Photos courtesy of George Iles

Ashburton Lakes

  • there are 12 lakes in total
  • they were formed by glaciers
  • the four main ones are Lake Heron, Lake Clearwater/Te Puna-o Taka, Lake Camp/Otautari, and Lake Emma
  • Lake Heron is the largest lake and is an important place for some endangered birds.

Braided Rivers

  • the Rangitata River is a braided river
  • braided rivers break into many strands (called braids)
  • the braids change over time
  • the Rangitata was formed by a glacier
  • the Rangitata River carries stones down the valley
  • braided rivers are great feeding and nesting grounds for native birds.

Audio Māori keywords: 

Create: Make a model to show how kettle holes are created.

Ō Tū Wharekai

Braided Rivers


The Rangitata River is part of the Ō Tū Wharekai wetland ecosystem. What type of river is it? Image: LEARNZ. 

A kettle hole at Ō Tū Wharekai. What time of year do you think this photo was taken? Image: LEARNZ.

Lake Heron is one of 12 lakes at Ō Tū Wharekai. How did these lakes form? Image: LEARNZ.

This plant will often be found growing around swamps - what is it called? Image: LEARNZ.