The dry weather that caused headaches for energy planners this winter has had a big impact on company profitability.
The after-tax profit for Mercury, formerly Mighty River Power, rose by 15 percent, while Genesis Energy fell by 36 percent.
Mercury raised its net profit after tax to $184 million. Operating earnings also rose.
The company was able to exploit dry conditions in the South Island to send high-priced power southward in large volumes from its Waikato River dams.
Meanwhile, Genesis Energy's net profit fell to $118.7m.
It owns part of the Waitaki hydro scheme in south Canterbury, which was exposed to the dry conditions, and it was forced to burn expensive fuel at Huntly to make up for hydro's deficit.
It was also hit by financing and restructuring costs.