Recently listed Mighty River Power saw total power generation fall 16 per cent in the June quarter because of the North Island drought.
MRP shares have disappointed investors since the company listed in May, slumping as low as $2.20 from an initial offer price of $2.50. The shares last traded at $2.40 yesterday before today's announcement.
MRP has released operational figures for the June quarter but will not issue its June year financial results until August 28.
MRP said its operating figures were "in line with company expectations".
In the quarter, sales to customers were down 3 per cent on the previous comparable period, with lower volumes to small and large commercial customers, although sales were up 5 per cent on the year.
The average price received from customers over the quarter was $126.76 per megawatt hour, and $117.28/MWh for the 12 months.
Total generation was down 16 per cent in the June quarter because of lower hydro power generation. That reflected lower than average inflows into the Waikato River.
In April, Mighty River Power had the lowest monthly hydro production on record, having started the quarter with storage at just 33 per cent of the historical average.
Water levels into the Waikato improved later in the quarter, which was expected as rain fell after the summer drought.
Storage was up to 79 per cent of the average by the end of the financial year.
Geothermal production in the quarter was lower than the previous quarter, mainly because of planned maintenance at the Mokai and Kawerau stations.
In addition to the 1379GWh total generation during the quarter, Ngatamariki has generated 61GWh during commissioning activity in the period, which was not included in the reported figures.
Gas-fired generation volumes were down because of lower wholesale market prices after higher inflows into other generators' South Island hydro catchments.