River Temperatures Autumn river water temperatures ranged from about 8°C in the southern South Island (lower in a few high altitude catchments) to >16°C in central North Island – generally showing the typical altitudinal trend super-imposed on a weak (S-N) latitudinal trend. River water temperatures were higher (by 1-2°C) than normal for autumn over large parts of the country, and were appreciably higher in Hawkes Bay and large areas of the South Island. Visual clarity of rivers reflects geology, soil, and land use patterns.