One last thing is that you can literally see most vertical current seams on the surface. A tactic that has worked well for me over the last couple of years is to sit at the top (upriver) of the seam in the slow water and cast the proper weight jig/plastic into the fast water. The right cast with the right jig will get the bait to swing into slow water close to the bottom and there the fish are waiting for just such an opportunity.
Another way I’ve done well is to use my trolling motor to move upriver in the fast water while I cast into the slow water … the jig will cover the slow water area (almost always a flat) as it swings out behind the boat.
John