A 3.7kg rainbow trout caught at Lake Okataina measured as opening day's biggest fish, while Lake Rotoiti offered the best conditioned fish, according to Fish & Game.

This year's fishing season kicked off on October 1 at Rotorua's three lakes, Tarawera, Rotoiti and Okataina.

Fish and Game officers, honorary rangers and other volunteers surveyed more than 600 fishers and weighed and measured their catches as they returned to boat ramps.

Fish & Game officer Matt Osborne said Lake Rotoiti provided the better catch rate and longer fish but weather on the day made it hard to fish at the lake.

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"Anglers who put safety first couldn't fish where they wanted in comfort, however Lake Rotoiti normally comes into its own in November," he said.

Lake Tarawera also had its problems as fish were returned to the water because they were considered too skinny to keep.

Fish caught at Tarawera averaged 481mm in length and 1.2kg, which was down from last year on average by 10mm and 160g in weight.

"The lake is going through tough times but steps are being taken to investigate the reasons behind this, and see if we can turn things around," Mr Osborne said.

"We are dealing with complex ecosystems that go through cycles and available food is only one factor among many in determining fish survival and growth."

Poor weather was a crucial factor at all lakes on opening day, but Mr Osborne said there was still ample time.

"There are plenty of people still out fishing and lots of opportunities are still on the way. Pick your days and get out there."