Total power generation by Genesis Energy fell by 29% in the first three months of this year and Meridian Energy's generation jumped 33% compared with the same quarter last year.
Both State-owned power companies were grappling with drought conditions in the quarter, but Genesis also had an outage lasting 13 weeks at its Tekapo hydro stations.
Genesis Energy's March quarter report says its hydro lake levels fell from 142% of the long run average in early January to 77% of the average by 31 March.
Most of its power sources are North Island-based.
Genesis general manager of corporate affairs Dean Schmidt says low demand meant less power was generated than usual.
He says there has not been the expected pick up in demand over the last couple of months because the weather has not been as cold as usual.
Meridian Energy says high rainfall in January gave it a higher market share, while low inflow in the following months was well managed.
The load of the Tiwai Point Aluminium Smelter, its biggest customer, was reduced to help manage low lake levels.