Over the past four years, 80,000 rainbow trout fingerlings have been released into the lake, and nobody seems to be catching them.

"It's as if they have all disappeared, all gone, because I don't know anyone who is catching any," treasurer Peter Byrom told the annual meeting of the Oberon branch of the Central Acclimatisation Society (CAS) last week.

"The quality of the released rainbow trout has been exceptional, yet no catches are being recorded. Some were even released in the upstream reaches of the lake."

It is almost certain that the culprit is the predatory redfin, which was unofficially introduced into the lake about eight years ago and is now the only fish being caught, mostly in sizes of 150 to 280 millimetres.

However, in its search for answers, the CAS branch - which each year stocks the district's waterways with brown and rainbow fry supplied by the NSW Department of Primary Industries' fisheries department - is about to try to solve the mystery with several initiatives.

The primary move will be to ask the fisheries department to carry out a fish survey to research if any trout are surviving.

The branch will also encourage feedback from anglers by launching a competition on its Facebook page, inviting fishermen to send in photographs of their catches, and offering a prize for the best fish picture.

And in a bold proposal, CAS will suggest to the fisheries department that Murray cod or trout cod could be a viable alternative in the lake to trout.

The organisation will seek a meeting with fisheries officers and Oberon Council officials to discuss grants to improve facilities at Reef Reserve and Kelly's Bay, with disabled and wheelchair access top of the list. 

A $40,000 DPI grant to CAS is available for the work, and Oberon council - which favours a boat ramp and wheelchair-accessible pontoon - has offered $20,000 as an in-kind donation.