Tailrace pools collect plenty of debris and baitfish, and there's no better locale to encounter highly active fish. Shoreline eddies can be caused by any and all of the aforementioned structures. What differentiates an eddy from a pool is simply size. For me, pools are small current breaks that can be covered with a cast or two, whereas eddies sometimes extend downstream for 50 yards or more. A good place to happen upon river eddies is along either bank just downstream of a major bend.
Bends commonly contain bars and major logjams that in turn create eddies.
Pools created by downed trees are there one day and gone another, but a typical eddy holds its form at least through the warm water months. High river levels combined with abundant floating timber during the spring thaw can literally redefine the contours of a small river. The shallow rapids-area mentioned earlier is another magnet for active fish. River fish often spend their day swimming back and forth between slack water and fast moving current. Gravel and small rocks comprise a typical set of rapids.