The general area of the park is bound by the Rangitata and Rakaia rivers. The headwaters of both rivers are notable landscapes, including the upper Rangitata which featured in the Lord of the Rings films (Mount Sunday was a location for Edoras).
The Canterbury Conservation Management Strategy acknowledges the area by stating ‘The overall character is one of space, remoteness and grandeur in an alpine setting of snow and ice, glacier and lakes, interspersed with remnants of upland forest, tussock grassland and several major wetlands.'
The Heron basin, Ashburton lakes and upper Rangitata are recognised as outstanding landscapes in the Canterbury Regional Landscape Study 1993. The Ashburton District Plan also recognises the Hakatere Basin as an outstanding landscape.
Kettleholes, found largely in the eastern South Island high country, are another distinctive landscape feature.
Threatened species present include plants such as pygmy forget-me-not (Myosotis minutiflora), a threatened sedge (Carex tenuiculmis), the critically endangered Craspedia ‘Heron’, and one of the largest known populations of a threatened native lily, Iphigenia novae-zelandiae.
The park, in an area alongside Lake Heron, provides protection for an extensive complex of kettlehole wetlands, very likely the best under protection in the country. Read about the Ō Tū Wharekai wetland restoration project
Associated with the kettleholes is turf vegetation, a rare habitat type on a national scale. Threatened turf-forming plants found here include pygmy clubrush (Isolepis basilaris) and dwarf woodrush (Luzula celata), both classified as in serious decline; and the nationally endangered water brome (Amphibromus fluitans), a semi-aquatic grass that grows in circular mats. Until last year this was presumed extinct in the South Island. Kettleholes also provide important habitat for water birds.
Both the Rangitata and Rakaia rivers have water conservation orders placed upon them. Braided riverbed habitat in the Rangitata is recognised as a habitat of national importance, containing many bird species - significantly wrybill/ngutu parore, black-fronted tern/tarapirohe, banded dotterel/turiwhatu, Caspian tern/tārā nui, and black-billed gull.
Wetlands in the park and contingent lakes are a significant stronghold for the threatened Australasian crested grebe/kāmana, and New Zealand scaup/papango.
The Mount Somers giant wētā Deinacrida, a spectacular and distinct wētā, was first discovered in the lower Woolshed Creek catchment in 1957 and rediscovered in 1995 in Woolshed Creek. Other notable fauna include the Mt Potts scree skink, a new species of skink discovered on Mt Harper / Mahaanui Range, native fish, and diverse range of aquatic and terrestrial invertebrates.
The park includes over 4000 hectares of mountain beech forest (former Mt Hutt Conservation Area) in the upper catchments of Dry Creek and Pudding Hill Stream. The forest is mostly mountain beech, with secondary species including broadleaf, Halls tōtara, fuchsia/kōtukutuku, marbleleaf/putaputāweta, kohuhu and pokaka, with crown fern and bush lawyer. Southern rātā, a botanical rarity in this part of Canterbury, is also found in places. Native birds likely to be heard or seen in the forest include bellbird/makomako, tomtit/miromiro, rifleman/tītitipounamu, wood pigeon/kererū and grey warbler/riroriro, while kea and pipits/pīhoihoi frequent the open country above the bushline.
Hakatere Conservations Area (Barossa)
At higher altitudes slim-leaved snow tussock grasslands and cotton daisy predominate. In gullies and boulderfields are regenerating shrublands containing snow tōtara,
mountain ribbonwood/houhere, matagouri, broadleaf/kāpuka and Coprosma species.
The significantly different vegetation on the western side of Stour River is a result of the rhyolite bedrock which occurs only here. The dry and rocky northern slopes have large patches of kānuka, with mänuka and a few Halls tōtara, snow tōtara and bog pine. The south-facing slopes have mountain beech/tawhairauriki in a few deep gullies and broadleaf and mountain ribbonwood in areas of boulder field.
Red tussock was probably once extensive in the wetter parts of the west Branch Stour River. The only remaining large area is at the southern end, where individual tussocks reach 1.8 m tall.
A variety of native birds are found in different parts of the area. In the tussock lands are New Zealand pipit/pihoihoi, New Zealand falcon/kārearea and Australasian harrier/kāhu. Waxeye/tauhou and grey warbler/riroriro occupy shrub lands. Australian crested grebe/kāmana, Australasian bittern/matuku, black shag/kōau and paradise shelduck/pūtakitaki can be found at Lake Emily and other wetlands.