The reason why you didn't catch fish is the area you were fishing. That zone behind the island sucks. It's pretty much void of fish.
Next time you go, set out from the beach and troll your fly over the dropoff parallel to the beach towards the doggy off leash area (the dropoff is very close to the beach, and very sudden).
Make sure your fly stays in the first 12 feet of water, which means a slime line 80% out at slow trolling speed would be perfect. Any fly will do, but black and olive micro-leeches work best this time of the year.
When you reach the submerged fence, turn 90 degrees to the north and head across the lake towards the big rock, staying parallel to the east end of the lake. Troll that stretch at different distances from the shore a few times. You will limit out in a couple of hours garanteed.
If you want to be adventurous, head all the way accross the lake to the North Beach and fish the north-west corner. The best bottom on Buntzen Lake is over there and likely the only area conducive to chironomid fishing. You can slowly troll the fly along the west 'wall'.
If it is large fish you are looking for, get a type 7 flyline and fish at 70' plus DOWN with the biggest and meanest wooly bugger you have.
Tight lines,
Milo