A tough year for Mighty River Power.

Record low hydro generation dealt a $52 million blow to the company in the last financial year compared to what it could have expected in an average year.

CEO Fraser Whineray says the company's operating earnings were down by four percent compared to last year.

Profit was $482 million - which he describes as robust in challenging conditions.

Net profit after tax was $47 million - which was $165 million lower than in the previous financial year.