When you mention seams in your post I`m not sure if you are making the distinction between seams and slots or not.
A seam is of course the interface between two currents of different speed. The friction between the two creates a seam of slower current sometimes even a backeddy. These are ideal lies for salmon which tend to lie on the slower current side. Seams are commonly formed when an obstruction occurs on one side of the water.Root balls ,down trees ,and channedl changes in direction which form seams at the break away point from the bank are always worth fishing.
In contrast a slot is formed when water passes between two obstructions usually rocks. A deeper channel is carved out in the slot and the colour of the water in the slot is usually darker and the surface is usually less broken than water at the sides of the slot. This is the premium steelhead lie; even current on both sides and cover from above . These locations should be fished heavily .