About 490MW of power - more electricity than is generated at the Clyde dam running at full capacity - is being sent south via the Cook Strait cable, as North Island thermal stations feed South Island power demand.
With lakes' capacity sitting at 58% of average, and no significant rain forecast for the next two weeks, Transpower, the national grid operator, has already started planning for a power conservation campaign.
Niwa released its seasonal winter outlook yesterday, and said although the La Nina weather pattern (which brought dry, hot weather over the summer) had concluded, there was little prospect for rain to fill lakes over winter.
Transpower spokeswoman Rebecca Wilson yesterday said a conservation campaign would begin if lake levels did not rise in the next three weeks.
Power generators were also talking to major industry users about cutting back on power use.
She said the weather forecast was not promising for the next two weeks, and every bit of rain would count.
The biggest problem was much of the rain would turn to snow and not end up in the lakes immediately.
Major industrial users, such as the Tiwai Point aluminium smelter, had already cut back on power use on the back of high spot power prices.
Power was being shifted south on the Cook Strait cable 99% of the time.
Lake levels were at their lowest since 1992, but power demand had increased by more than 1000MW since then.
Planning for the conservation campaign had already begun, to be set to go in three weeks' time, but she said voluntary measures would be used.
She could not guarantee there would be no black-outs but said the power industry was doing all it could.
The Niwa forecast predicted a 20% chance of above-normal rainfall for the west and south of the South Island, where the hydroelectricity lakes are.
In more bad news for householders, fuel prices are expected to remain high, with retail prices yet to catch up with the price of raw product, which will affect diesel heating costs.
Diesel prices are $1.74 a litre, an increase of 39% since the start of the year.
Shell spokesman Jackie Maitland said the price of raw crude product had risen 18% in the past month, yet the price at the pump had only risen by 6%.
Fuel companies were trying to do their best for customers.
Diesel rose 71c in the past year, including 27c last month.
How to save power:
Switch off appliances at the wall.
Use heated towel rails sparingly.
Turn off a second fridge.
Dry clothes outside on the line.
Rinse dishes only under cold water.
Close curtains just before dark.
Use the right-size saucepan for element.
Fix dripping hot taps.
Use thermostats and timers.
Use energy-efficient light bulbs.
SOURCE: EECA
