A part of the Wye I sometimes fish below Rhayader runs through some quite rough terrain and creates some stunning scenery but as a consequence the wading is quite treacherous in parts and a wading staff is an essential part of your gear.
I also think these more dramatic stretches of water are where you can sometimes find better quality fish, I think the high oxygen levels combined with deep gutters for the fish to hide and of course a good food source all combine to produce an ideal habitat for the odd specimen fish.