I have huge success in high country lakes and even in the big low valley Okanagan Lake with believe it or don't a #12-#14 pheasant tail nymph. I caught a 14lb4oz Rainbow out near the middle (a mile from shore ) Okanagan lake on a #14 nymph fished with a #7sinking line (not a 7 weight line) #7 is the heaviest sinking line in a 5 weight. I was trolling 2.2 mph which is best for trout about 1.5mph for kokanee (land locked salmon)
If upon inspection I find the trout stomach is full of minnows I use a black doc spratley with silver wraps.
a red Dawl bach is also one of my go to lake patterns.