Wanganui River mouth from Mt Oneone, near Harihari, Westland

The Wanganui River, near Harihari, is a classic West Coast river. Beginning in tributaries high in the snowfields and glaciers of the Southern Alps, the river quickly gathers strength as it descends precipitously through steep, boulder-choked gorges to eventually cross the Alpine Fault at the western extremity of the Alps. From here the river leaves the mountains behind, taking on a wider, more braided form as it crosses the narrow Westland coastal plain on its way to the Tasman Sea. At its mouth the river fans out into a broad estuary and wetland area which is of national significance for its abundant plant and bird life.

Enormous glaciers scoured this same area during past ice ages, depositing millions of tonnes of moraine westward of the Alps and extending the coastal plain itself. While much of this moraine has been reworked by rivers since the end of the last ice age, many remnant deposits and large blocks of moraine remain intact and the isolated Mt Oneone, overlooking the Wanganui River mouth and estuary, is one such remnant.

Mt Oneone is one of only a few places in New Zealand where a steep hill exists immediately next to a significant coastal wetland area. A short 45-minute track takes walkers to the top of Mt Oneone, where a lookout offers an impressive panoramic view over the entire Wanganui river mouth and its associated estuary and wetlands.