Not far from where i live , not a fishery but a private lake already lost a lot of good fish the past few years . Otter fencing is the only way to be as sure as you can of keeping them out & protecting your fish. But not all lakes can do this.
We are going to put an electric fence up thus week which might save the odd kill but it's not fool proof , I've got enough spare from my sheep to set one up , proper otter fencing with an over hang is what you need but we can't do it there due to not owning it outright , just the fish !!!