The latest information on hydroelectric lake levels supplied to Energy Minister Pete Hodgson shows a further slight increase in storage due to higher inflows.

Mr Hodgson is getting regular information on hydro lake storage and is releasing weekly updates.

In the week to 18 June storage increased slightly to 69 per cent of the average for the time of year. Last week it was 63 per cent. Inflow to the lakes was 78 per cent of average, compared to 68 per cent the preceding week.

"This improvement in total storage is welcome but not substantial enough to significantly reduce the risk of supply shortages later this winter," Mr Hodgson said.

"Crucially, the lakes feeding the Waitaki system remain close to their minimum levels. The Waitaki is New Zealand's major source of hydroelectricity and its lakes must rise substantially before our level of comfort about security of supply can increase.

"Wholesale electricity prices shot up again yesterday after dropping in recent days, partly reflecting higher North Island power demand.

"This is the first dry cold winter in which the wholesale market has operated with the industry in its present form. The market is facing its first hard test and New Zealand is finding out for the first time how it responds to supply pressures."

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