Continued low inflows into Clutha River hydro-electric dams have forced generator Contact Energy to turn to North Island gas plants to fill the gap.
Last month, Contact head of hydro generation Boyd Brinsdon said inflows in the previous three months into its power stations on the river were as low as they had been since recording began 80 years ago.
Yesterday, he said the problem continued, meaning Lakes Wanaka and Wakatipu were still at low levels for the time of year.
Yesterday, Lake Wanaka was at 276.5msl (meters above sea level), Lake Hawea was at 338.5msl and Lake Wakatipu sat at 309.4msl.
''Hawea is about half a metre above the bottom of its normal 8m operating range.''
Contact would only let the lake go below 338msl if Transpower announced a security supply risk.
''If we don't get any rain they will just continue to decrease. We've had a few weather cold fronts recently and when they're from the south they're cold and snow tends to fall instead of rain.''
A comparatively warm day such as yesterday meant some of this snow would melt, stopping lake levels from falling any lower.
A cold front that swept the country last week sparked a ''dramatic'' increase in electricity demand, which meant more water was taken from Lake Hawea ''than was ideal''. Now the front was gone, Contact could lower those takes.
Some rain was forecast for the end of the week, which would ''slightly'' increase flows, Mr Brinsdon said.
The low inflows meant Contact was pushing its North Island thermal plants harder to supply the South Island and the Cook Strait cable continued to supply more North Island energy to the South Island.
Contact had several thermal gas stations in the North Island and Genesis Energy's plants ran on gas and coal.
''This is the way the New Zealand electricity market is designed to work. We strive as an industry to be as renewable as we can, but when you've got a system that relies on the weather for both water and wind, you need other types of energy.
''My belief is that you can't have a completely renewable system. You need something like thermal to fill those gaps when the weather gods don't play ball.''
Historically, rain tended to fall from September, but in recent years it had been relatively wet in winter, he said.
''So in some ways this is a return to normal conditions.''
