Hot weather threatens hydro lakes

The warm, dry weather has power companies on alert, as they keep a close eye on the hydro lake levels in the South Island.

The hot weather is taking its toll on Lake Pukaki, one of the country's largest hydro lakes.

One of the reasons the lake is so low is that the hills in the Mackenzie country are bare of snow - melted away in the blistering sun.

There's also been a lack of decent rainfall in the last six weeks. Power authorities are keeping a close watch on falling lake levels.

Mike Roan of Meridian Energy says the future is uncertain.

"The summer period is when we expect it to rain a lot down in the South Island and so we still expect that to occur."

Hydro electricity accounts for up 65 percent of New Zealand's power generation.

Lake Tekapo and Lake Pukaki rely on winter snow storage and westerly rains in the mountains to top them up. 

Electricity Authority CEO Carl Hansen says there's no cause for alarm. 

"Relative to average, the lake levels are somewhat low, but the industry has been operating using lots of different sources of generation to conserve the hydro lake levels."  

Authorities say consumers shouldn't be concerned.

The electricity industry is increasing its response to the hydro lakes situation, using sources like coal and gas, while the Cook Strait inter-island link is running more power south than usual.

Generators are desperately relying on rain for the coming winter. A tropical storm forecast later this week will bring some relief. 

Mr Roan from Meridian remains confident about the situation.

"There's still plenty of summer to come and we still expect it to rain."