He said growing conditions for trout in Okataina had been very good in recent years.
"Combine this with lower angler pressure as a result of lake levels and boat launching issues, and you have a formula that means trout can grow to a larger size before they're harvested."
Mr Osborne said with Fish & Game's Fish for Gold promotion underway this year, he hoped to see more anglers fishing on Lake Rotorua, too.
A total of 40 red-tagged fish have been released, 10 each, into lakes Tarawera, Okataina, Rotorua and Rotoiti.
Anglers who have registered for the event can win a grand, one-off prize of $25,000, or catch a fish carrying a prize worth $200. Anglers must have a current licence and register to be eligible. Entries are limited to the first 1200 people to enter, and the deadline to register is September 30.
-The traditional haggis ceremony will take place at The Landing at Lake Tarawera from 5pm tonight, with bagpipe players, whisky, Scottish dancing and a blessing of the boats.