In water shallower than that, the technique may spook more fish for you than you catch. Fish don't have to see your boat to know it is there. At the very least it puts the fish on alert. Very few big fish are caught by vertical jigging in shallow water. Very few big fish are caught in river systems by vertical jigging at all.
Cold water is much denser than warm water.
It transmits sounds faster and louder and no electric motor is soundless. So that brings us to the over-looked anchor. Anytime you can pin-point fish in shallow water, you should consider presenting your bait from an anchored position. On lakes I know very well, I know where the shallow fish-attracting structures are. The best approach is often to drift into position, carefully and quietly set down the anchor and begin fishing by casting.