Meridian Energy general manager wholesale Chris Ewers said Lake Pūkaki had been at below average levels for more than 150 days before the recent bout of heavy rain.
"All the rain we missed from April to August finally arrived in September," Ewers said.
"We’ve been managing our hydro lakes extremely carefully for months now, but there’s nothing like a helping hand from Mother Nature."
Over the last week, Lake Pūkaki rose 715mm to just over 525m above sea level - 102% of average for this time of year.
"The last few weeks have more than exceeded our expectations," Ewers said.
"The Waitaki catchment, which feeds Lake Pūkaki and the Waitaki Hydro Scheme, had its fourth wettest September on record."
Heavy snow in the mountains was also welcomed as it feeds the lakes throughout the warmer summer months.
"After a challenging winter, we couldn’t have asked for a better start to spring."
The average North Island wholesale or spot price was down $5 to $78 per megawatt hour. In the South Island, it dropped $5 to $69.
