Some diesel from the September spill at Turoa may have found its way into the pristine Manganui o te Ao River - but testing by Horizons in early October found none.
The September 27 spill of 19,000 litres of diesel from a tank at the ski area saturated ground and entered the Makotuku Stream, Raetihi's usual water supply.
The Makotuku is diverted by New Zealand Energy (NZE) to generate electricity. Up to 25,920 cubic metres of water can be taken from it every day.
The spilled water then flows into the Orautoha Stream, then the Manganui o te Ao and then the Whanganui River, potentially allowing diesel through into them as well.
The Manganui o te Ao is famed for its trout fishing, blue ducks (whio) and unspoiled riverside camping at the Ruatiti Domain. It is also the subject of a Water Conservation Order, the highest level of protection that can be afforded to any water body.