The glacial processes that shaped the landscape of Ō Tū Wharekai created a range of habitats – kettleholes, swamps, fens, seepage wetlands and marshes, as well as a network of freshwater lakes and braided rivers.
Not usually thought of as a typical wetland, dynamic braided rivers provide nationally important habitat for a range of threatened native birds, fish and invertebrates. Ō Tū Wharekai contains some of the best examples of high-country lakes in New Zealand. In their natural state the lakes are dominated by native aquatic plants which regulate water quality and support aquatic wildlife.
The relatively pristine braided rivers and streams of Ō Tū Wharekai make it a highly valued wetland system. However, the ecosystem is threatened by the expansion of exotic plants, introduced predators disrupting native animal communities, and land use changes affecting water levels and quality.
Ō Tū Wharekai is an important site for kettleholes. These distinctive features are made when retreating glaciers leave behind large blocks of ice which leave a hollow when they melt. Kettleholes may fill with water during wet seasons, providing habitat for ephemeral turf.
The kettleholes at Ō Tū Wharekai support rare turf vegetation like pygmy clubrush (Isolepis basilaris) and dwarf woodrush (Luzula celata), both classified as seriously declining. The nationally endangered water brome (Amphibromus fluitans), which was until recently presumed extinct in the South Island, is also found in the kettleholes.
Lake Heron is the only site in New Zealand where the critically endangered Craspedia ‘heron’ is found. Other threatened species include the endangered marsh arrowrush (Triglochin palustris), pygmy forget-me-not (Myosotis minutiflora), and one of the largest known populations of the iphigenia native lily. A threatened species of sedge (Carex tenuiculmis) is found in the swamps.
The freshwater lakes support a huge range of native and exotic aquatic plants. Native species like Chara australis and Nitella pseudoflabellata feature in charophyte meadows in lakes of high habitat value, such as Lake Clearwater and Lake Camp.
The lakes, rivers and wetlands provide habitat for over 30 bird species. The braided rivers are breeding sites for the threatened wrybill/ngutu parore, known for its unique laterally curved beak, and for the kakī/black stilt, one of the most endangered birds in the world. The black-fronted tern/tarapirohe, banded dotterel/turiwhatu, Caspian tern/tārā nui, and black-billed gull can also be found in the wetlands and rivers, as well as various species of waterfowl, bittern/matuku, and the Australian crested grebe/kamana.
Tadpole shrimp are found in the kettleholes, and longfin eel/tuna live in the lakes, streams and wetlands. The lakes also provide habitat for freshwater mussels/kākahi, which play a crucial role in filtering the lake water.
Ō Tū Wharekai has the highest diversity of lizards in New Zealand. The greywacke scree slopes of the mountains provide a home for the elusive scree skink, a large-bodied reptile found only at a few sites in the South Island. Like many other lizard species in New Zealand, the scree skink is rare due to mammalian predation.
History and culture
Early Māori lived in a major kaik (village) in the area. “Wharekai” means the dining hall of a marae, an apt name for the fertile wetlands which provided abundant mahinga kai. Resources included tuna (eel), weka, kākā, kokopu, tūī, pūkeko, kākahi (freshwater mussels), kiore (Pacific rats), aruhe (bracken), tikumu (mountain daisy) and ti kōuka (cabbage tree).
The area was also part of the pounamu trails and an ara (path) to Poutini (West Coast).
Through the Ngāi Tahu Settlement Act 1998, a Statutory Acknowledgement and Deed of Recognition is in place over the area to formally acknowledge the association and values Ō Tū Wharekai holds for Ngāi Tahu.
Working with iwi and hapū to restore wetland values is a key objective for Arawai Kākāriki. DOC is working in partnership with Te Rūnanga o Arowhenua, who have completed a cultural health assessment of Ō Tū Whareka (on the Takiwā website).
Working with others
Working with the community and increasing public engagement is an important objective for Arawai Kākāriki. Ō Tū Wharekai has a long history of community involvement in conservation work.
- Environment Canterbury is involved with Arawai Kākāriki’s restoration efforts.
- The Lake Clearwater Hut Holders Association has fenced and re-vegetated 400m of riparian margin next to the Lake Clearwater village.
- Rangitata Landcare Group was set up by adjacent landowners, territorial authorities and DOC in 1999 to control broom in the upper Rangitata River.
- Forest & Bird and the Ornithological Society have been carrying out annual winter waterfowl counts since 1984.
- Mid-Canterbury Forest & Bird hold annual wilding pine working days around Lake Heron.
- The local community have also been involved with many working bees, such as planting in the riparian margins around lakes.
- The Arawai Kākāriki project regularly hosts primary and secondary schools and tertiary institutes, and the Aoraki Polytechnic Outdoor Recreation course involves students in conservation projects.