The Manawatu-Whanganui regional council is to prosecute Ruapehu Alpine Lifts and Petroleum Services Limited for a diesel spill into the Makotuku Stream in October last year.
Up to 19,000 litres of diesel leaked into the Makotuku stream in Tongariro National Park from a tank at the base of a skifield run by Ruapehu Alpine Lifts.
It forced Raetihi's water supply to be shut down for several weeks.
Council spokesperson Nic Peet says it has completed a thorough and lengthy investigation.
Mr Peet says given the impact of the spill on the Raetihi community, the council will take a prosecution to the Environment Court.