I like to go on the 15th of July. This is the opening date for the Yellowstone River and there is also a nice Callibaetis hatch on the Lake.
Take a float tube, or pontoon boat and start fishing in Bridge Bay at daybreak using a large black Wooly Bugger with a trailing size 12 Callibaetis PT nymph. I like one that uses an olive marabou body. Just take four marabou fibers, tie in at the tips and palmer up to the thorax for a natural taper. You will catch 98% of the fish on the nymph, but the bugger is an important attractor. Fishing will be fast! You can switch to dry around 9:30 if you want, but I've found I get better results sticking with the nymph. I use a floating line and 12 foot leader/tippet combo. The wind starts blowing at 11:00 and by 1:00 you will want to get off the lake. Bridge Bay is protected a bit, and the wind blows toward the shore, so it is a fairly safe place to fish. The river is also great, but gets a little crowded. The fish sometime come right into the shallows for a size 16 lite colored mayfly. Sometimes there will be a bunch of fishermen standing out casting into the main run with fish slurping mayflies behind them! It is fun to see their startled looks when they hear the splashing of a fish you just hooked in 2 feet of water! At night there is a spinner fall and hundreds of fish sip the spinners, but it is frustrating fishing with few hook-ups. The Gibbon river is a fun dry fly stream, large attractors work well. Have fun!
