The third-quarter operational update showed hydro generation was about 50GWh below average at 843GWh, although that was still 136GWh more than the previous corresponding period.
Geothermal generation was again strong but there was little variance in geothermal generation from period to period, unless something had gone wrong, he said.
In its commentary, Mighty River pointed to an issue of premium generation prices it used to receive - by hitting peak prices - being less in the future.
Electricity customer numbers were down 3000 in the quarter and Mighty River was at present losing more customers than any other retailer, despite its efforts to move customers to a fixed-term contract, Mr Foster said.
Mighty River reported its Mercury subsidiary had 43% of its customers on fixed-price contracts, due to more than 28,000 customers taking up a two-year offer in preference to an increase in energy prices.
The average electricity energy price to customers was $110.10/MWh, 1% lower than the pcp due to the yields for new commercial contracts being below those now rolling off.
‘‘A little curiously, Mighty River claimed third-quarter national demand increased 0.5% on a temperature-adjusted basis.
‘‘Contact and Meridian Energy data showed national demand down over the quarter, as does our data, and intuitively a hot summer should have increased air conditioning load. We are not sure why Mighty River is effectively claiming a hot summer should reduce demand,'' Mr Foster said.
Overall, the slightly disappointing numbers from Mighty River were likely to lead to a modest downgrade from Forsyth Barr's 2016 operating profit forecast of $493 million. Mighty River's guidance range was $480 million to $500 million.
The current target price was $2.70 a share and the rating was underperform, he said.
