The wetlands occupy a basin that has been down-faulted in the underlying schist, a metamorphic rock that still outcrops as the ‘islands’ within the swamp. Over time, the Taieri Plains accumulated river sediment, overlain by peat in the poorly drained parts. Today, the shallow lakes, Waihola and Waipori, are linked by water channels and their deltas, fed by fresh water, but also subject to slight tidal influence at their downstream parts. The wetlands can be classified as swamps, i.e. relatively fertile, with much surface water and numerous ponds.
Within the swamps the main plants are ten species of Carex sedges (so-called ‘cutty-grasses’), shrubs of mingimingi (Coprosma propinqua), and fans of harakeke (N.Z. flax, Phormium tenax). The slightly higher ground of river margins hold more trees and shrubs, including cabbage trees (tī kōuka, Cordyline australis), while water margins have dense reedlands of raupō (Typha orientalis) that extend as rafts out across the water. Numerous aquatic plants provide food for ducking and diving waterbirds.
Whakaraupuka (Ram Island) and Lonely Island still hold remnants of the original native bush. Restoration of forest is now well underway, as weedy gorse and broom scrub are being replaced by plantings of a large range of native tree species, especially, in the pioneer stages, kōhūhū, broadleaf, kānuka, kōwhai, lancewood, and koromiko.
Within the Sinclair Wetlands 131 native plant species have been recorded, still outnumbering the 77 naturalised plants. Only some of the latter are troublesome weeds. Willow and alder trees have been the subjects of a major recent aerial weed control across the wider wetland system. Individual outlier trees are the targets for ongoing control on-the-ground. The main weed of water margins and wet swampland is reed sweetgrass (Glyceria maxima) that can choke waterways, and poses an ongoing challenge for control.
At least 46 bird species are present in the area. In particular the waterbirds: paradise shelduck (pūtangitangi), grey teal (tētē), shoveller (kuruwhengu), New Zealand scaup (pāpango), grey duck/mallard hybrids (pārera), Canada geese, black swans, pūkeko/pākura (swamp hen) are all permanent residents of the wetlands.
The wetlands are also an essential habitat for the threatened Australasian bittern (matuku) and marsh crake (kotoreke). The shy fernbirds (mātātā) are thriving in this habitat, and can regularly be heard and seen along the walkways.
Other waterbirds frequently seen are white-faced heron, pied stilt, South Island pied oystercatcher, spoonbill, kingfisher, little shag, black shag, black-backed gull, red-billed gull, and feral geese.
You can see or hear native fantail, grey warbler, tui, bellbird, silver eye, swallow, pipit, morepork, harrier hawk, and shining cuckoo. Falcon, kereru and brown creeper may sometimes be seen passing through the area.
Introduced species that have made a home here are blackbird, thrush, starling, skylark, magpie, and the finches (sparrow, dunnock, chaffinch, greenfinch, goldfinch, yellow hammer, redpoll).
More information about individual birds can be found at New Zealand Birds Online, the digital encyclopaedia of New Zealand Birds. You can also enter your own bird sightings online at the EBird database.
Apart from the birds and the bees, the wetlands have numerous other creatures both above and below ground, upon the water and underwater. The ponds are the ideal home for tuna, especially the short-finned eel, which is typical of lowland waters. Whitebait (inanga) that have spent their youth in the sea, re-enter the wetlands, mainly in spring, to then become pigmented for camouflage in murky freshwaters. Once mature, they lay their eggs on the foliage of water-margin grasses and sedges, and continue to grow larger as kōkopu (which comprise several species of Galaxias).
In the silty beds of water channels freshwater mussels (kākahi) are a food source for eels, and were once regarded as ideal food for children and the sick. Freshwater crayfish (kōura) are present also, living among and feeding upon organic detritus at the bottom of water bodies.
Numerous invertebrates live in the wetlands, from tiny flies that have aquatic larval stages, to the more obvious giant dragonflies and tussock butterflies. There are spiders too, and none more obvious than the nurseryweb spiders that make conspicuous white nests on the mingimingi shrubs, each one enclosing numerous spiderlings.