Back to the path of least resistance, as promised a week or so ago. This time of year, smallmouth bass are migrating to habitats where they can survive the winter, and I've been following those migrations closely in Midwestern rivers for 40 years — along with the migrations of steelhead, muskies, walleyes, salmon, and brown trout, which also take up a considerable hunk of my time every year. Migrations of all these fish take on some similar characteristics.
Fish migrating in rivers against current tend to stick to the banks, especially on the side of the river where current is reduced, when possible. Which side has reduced current? The setting used to get upstream with your trolling motor can show you the difference, but you can see it with your eyes this time of year. Look for places where the leaves caught in the surface film are travelling slower.
Rivers want to travel in a straight line but the earth won't let them, forcing them to follow a serpentine path around immovable hills of rock or other resistant materials. When the river bends, flowing water hits the outside of a bend with the most force, digging deeper holes there. Current is reduced so much on the inside of the bend that sediment actually falls out of the flow to the bottom. Over time, those deposits make it much shallower on the inside of the bend — yet that's where fish would travel when going upstream if they had their druthers. However, security is a big factor. If the water is too shallow, they feel vulnerable and exposed, and will stick to the depths adequate for hiding them as close to the inside of the bend as they can get, and that goes for pike, carp, muskies, steelhead, salmon, bass, dogfish, walleyes, and every other species of fish I've had the pleasure of chasing during migrations.
Downstream migrations, as mentioned in that post a week ago, are different. Fish don't have to fight the current. Quite the opposite. They allow the current to help them slide downstream. As such, fish migrating in that direction are much more likely to utilize mid-river feeding zones and current breaks. They tend to hold on mid-river bars, and shoals for a few hours or a few days — maybe longer, if the weather holds. (Rapid drops in water temperature tend to herd the fish along.) The difference is quite noticeable. Even in very low water, you tend to find bass migrating upstream using shoreline oriented lay downs, points, inside turns, and bridge abutments more often. And even in water that's a bit high, you tend to find more smallmouths using mid-river structures and current breaks as feeding zones.
To find bass in a river this time of year, you need to know which way they're headed. If you have no idea where they spend the winter, it's hard to track them down during fall with consistent success. You may luck into a few spots where the fishing is really good, but don't count on those spots being good forever. Nothing changes faster, in the world of fishing, than a river. I've found bass so thick on certain spots you could catch double-digit numbers day-after-day for weeks, but in following years, bass never seemed to use that spot again. Often we can't perceive what changed, but something did. Something made the forage stop using the spot, or some sediment covered the gravel or clay that supported the crayfish, or some other change occurred that we can't see.
Learn which way the fish are going? Sounds pretty simple. And sometimes it is, but one way or another, it's a major clue to specific location during periods of migration.