South Island hydro lakes are lapping their crests after recent heavy rainfalls in the mountains and excess water is being spilled, which power companies view as a good situation just before winter.
Meridian Energy, which operates eight power stations on the Waitaki River and one at Lake Manapouri, was spilling water from four of its lakes yesterday, external relations manager Claire Shaw said.
At Lake Tekapo, 45cumecs was being spilled, 140cumecs at Lake Pukaki and 200cumecs at Lake Benmore. The Environment Canterbury website said last night 129cumecs were being spilled from Lake Ohau.
As the height of the inflow would occur yesterday, Ms Shaw expects the flows to increase.
She described the volumes of water being spilled after the "freak" rainfalls as "phenomenal".
Lake Tekapo rose more than 1m over 19 hours and Lake Pukaki just under 1m yesterday.
"At least we are going into winter with full lakes - very, very full lakes," Ms Shaw said. "We don't anticipate having any shortages of water."
However, higher lake levels would not impact on the price of power, as there were long-term pricing plans in place.
Contact Energy communications manager Jonathan Hill described the southern lakes as being in a "much better state than this time last year". The company's South Island hydro lakes, feeding the company's Clutha River power stations at Clyde and Roxburgh, were operating at 130% of their average levels, compared with 50% of average at the same time last year.
A "deluge" on Monday night resulted in a "small amount" of water being spilled, he said.
"There was such a wall of water that came into the catchment it needed to go down the river," Mr Hill said.
With winter not far away, the "very full" lakes meant the company could not see any supply issues for the season but Contact was still conscious of advising consumers to be careful with power use.
The ability to send any excess power generation north was hampered when the HVDC cable, linking power between the two islands, failed on Monday night.
Energy Minister Gerry Brownlee said the incident highlighted concerns about the state of the country's transmission network and its fragile security of supply.
The transformer failure means only one of the two inter-island links, or "poles", is operating.
Transpower could take up to a week to repair the fault.
"It does mean for the next two to seven days we're going to have somewhat less than secure supply, but it shouldn't mean any cuts or other type of activity," Mr Brownlee said.
• Police yesterday warned anyone camping in low-lying areas of the Waitaki Valley to be aware of rising river levels and take precautions.