Contact Energy Ltd lost 2000 electricity customers in the past month and 6000 customers in the past year, according to its latest operating report.
The company had 476,500 electricity customers at April 30, down from 478,500 at March 30 and 482,500 at April 30 last year.
The number of gas customers was 64,000, unchanged from March and down from 67,000 in April last year.
Competition for customers was intense in metropolitan areas and was continuing to creep into selected regional areas, particularly where Contact and TrustPower were incumbent operators, Goldman Sachs JBWere NZ analyst Matt Henry said in a commentary on industry customer statistics.
The market would continue to be competitive.
Contact Energy said North Island lake storage was 49 percent of mean levels in April, down from 71 percent in March, while South Island storage was 142 percent of mean, up from 102 percent.
North Island storage has since fallen to 34 percent of mean, while South Island storage is 139 percent of mean.
Mr Henry said the recent deluge in the southern hydro lake region had weakened the near-term outlook for wholesale electricity prices as lake storage levels have jumped. Lower wholesale prices would promote further competition in the retail market.
Pole One of the HVDC inter-island power network link has been operating intermittently but was expected to operate consistently through most of the winter when transmitting from the South Island to the North Island.
The company's power stations received an average $79.29 a megawatt-hour in April, down from $112.09 in March but up from $39.12 in April last year.
Generation declined to 756 gigawatt-hours in April, from 806 gigawatt-hours last year.
Contact Energy's nine power stations generate around 25 percent to 30 percent of New Zealand's electricity, according to the company's website.
