I have an older model Patagonia Double Haul pack that has worked very well for the past five or so years. The back part of the pack fits on my back at an angle and even when I stuff the back section with a water bottle and a rain parka, the front pack stays put. One of the things about this pack that I really like is that I can adjust the straps so the pack stays above the water when I wade deep.
Waist packs a great as long as you are not wading in water above your waist.