Anything above or below that magic number will make them sluggish, and their feeding will drop off. And that is where the difference between river bass and river rainbows ends and the fun begins. The rainbows on the main stem of the Upper Delaware River, unlike the browns on the West Branch of the Delaware River, can be found, for the most part, in the fast water. Pockets, riffles, rapids that's where they hang out. These fish want oxygen, and they want food, and that is where they will find it not in the flats and not in the center of the pools.
Smallmouth bass relate to river structure in much the same way as the wild Delaware River rainbows.
Many clients of mine are surprised to find smallmouth bass inhabiting the fast-moving skinny water of two feet. When the water is above 70 degrees in the middle of day that is where you'll find them. Plenty of food gets washed into these areas, and the fish are waiting for an easy meal. Travel north of Callicoon, where the water is usually a bit cooler due to the reservoirs. This time, instead of offering the fish a big meal, scale it down to include something smaller.