When fishing on a bright sunny day always try and fish the shady areas, such as under a log or under low-hanging trees. These areas will be protected from the sun's rays and will also be the dark shadows fish like to hide in so they can do their ambushing. Find the deeper areas in the river to fish. THese will be the areas that have the cooler water. This is where you'll probaly find one or two fish lying around beating the heat.
Fish become very lethargic and dont want to chase down a meal.
So presentation, specifically, slower presentation, is the best bet. Fish mainly in the early morning hours or the latter part of the evening. The temperatures will be cooler and predator fish, such as walleyes will be more active. Try to fish on overcast days, such as days when it is about to rain. The clouds will provide lower light levels, which the fish will use to their advantage when hunting food.