Meridian Energy says there are no plans to cut power prices, even though the hydro lakes in the South Island are full.
The state-owned power company says commercial customers who are buying electricity wholesale will be reaping the rewards because spot prices have fallen to as low as 1 cent per megawatt hour.
However, it says residential tariffs have to take into account a massive fluctuation in spot power prices, which were as high as $500 per megawatt hour last winter.
The company was planning to spill water from two more of its hydro lakes on Thursday night, after more rain was forecast for its lake catchments.
It was already spilling water from lakes Tekapo, Benmore and Pukaki, which are unusually full for this time of year.
Meridian spokesperson Claire Shaw says excess water would be released as well from Lakes Aviemore and Waitaki, for the first time since March 2004.
Ms Shaw says the high lake levels have come at a time when there is a reduced demand for power.
The company also says it is too early to say what hydro storage levels will be like next winter.
Consumer groups are calling for Meridian Energy to pass on savings to its customers.
The Domestic Energy Users Network says Meridian should offer cheaper power at a time when householders are hurting financially.
Consumer New Zealand research manager Belinda Allan says companies are often quick to put their prices up, but are slow to reduce them.