It was the lowest level for a June month since 2008. Inflows were 94% of average in June but that was skewed to the North Island.
Forsyth Barr broker Damian Foster said the low levels meant Meridian Energy called its swap option with Genesis, and continued strong electricity demand in June led to high wholesale prices.
Benmore averaged $117.80 a MWh, nearly twice the May average.
Lake levels should be sufficient to get through the winter and the short-dated ASX futures prices were only $3 MWh higher than the long-dated prices at Otahuhu, highlighting the industry was not greatly concerned, he said.
Wholesale electricity prices had shown a visible trend upwards as temperatures cooled and the low hydrology conditions continued. Prices peaked on June 21 due to a combination of high demand and low wind generation.
Mr Foster said South Island hydro catchments remained well below average.
Contact's Clutha catchment was just 27% of average on July 6.
The country's largest storage lake, Pukaki, was 54% of average and Meridian's Manapouri catchment was the only lake to add storage in the month.
Mercury Energy was likely to have a strong end to the financial year as Lake Taupo was the only hydro catchment with above average storage at 121% of average, he said.
Electricity demand, excluding New Zealand Aluminium Smelters, was again strong, up 5.2% in June against the previous corresponding period.
Maximum temperatures across main cities averaged 14.2degC, the coldest start to winter since 2013.
Customer churn, or people changing providers, bounced back above the 12-month average from low April levels.
The Electricity Authority started its What's My Number campaign in June which could lead to a further increase in churn.
This month, SaveAwatt released its offers to 12,000 households who signed up to its bulk switching programme, Mr Foster said.
SaveAwatt chief executive Tim Rudkin said the dry winter and rising wholesale prices might have affected retailers' offers into the programme.
He also noted falling hydro storage and rising spot prices might have made the scheme's offers more attractive to price-exposed Flick Electricity customers.
Mr Foster said Flick and Electric Kiwi backed up another month of strong gains, adding 1353 and 1075 customers respectively in May.
As a spot price provider, and if current market conditions persisted, it was expected to become increasingly difficult for Flick to maintain customer gains. Pulse Energy also had solid customer growth, adding 790 new connections during May.
Genesis had lost customers in 15 of the last 16 months, losing 2589 connections in May, its largest decline since April 2014. Mercury and Meridian also recorded customer falls during the month. Contact added 526 customers in May, and was the only large generator-retailer to record gains.
Looking ahead to the election, Mr Foster said Labour leader Andrew Little indicated Labour was sticking to its 2014 election policy of charging farmers a royalty for water.
The policy goal was to clean up New Zealand's rivers so they were suitable for swimming and, where fair, charge a fee on use of public water in large quantities for private gain.
New Zealand First had stated its support of the wider royalty on commercial uses of water.
