Evenings are best for surface action.
Caddis and other dry patterns work then, with Woolly Buggers fished deep most effective during the day. Elevation is 8,000 feet or more. It's a good sized lake for southern Utah, with primitive camping around the lake. Go to Hurricane and through Virgin, an hour from St. George. Float tubers are taking fish on Woolly Buggers in brown or olive on sinking lines.