Make a guess as to depth and then set the depth at 1 to 2 feet above the bottom. Drift it through. If nothing happens, lower the jig a foot or two and do it again. Repeat this until you either tap bottom or hook-up. I keep the jig 1 foot above the bottom if I know the depth and sometimes two feet if it's snaggy.
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If every fisherman would pick up one piece of trash, we'd have cleaner rivers and more access.