mighty river power was established on 1 april 1999, when the 1998 reform of the electricity sector took effect. the electricity corporation of new zealand (ecnz) was broken up into three state-owned generating companies - mighty river power, genesis energy and meridian energy. mighty river power took over the ownership and operation of the eight hydroelectric power stations on the waikato river, new zealand's longest, and also inherited the assets of two largely decommissioned oil-fired power stations at marsden point, near whangarei.