The best depth for lake trout is determined by water temperature. Find water that’s between 40 and 50 degrees and that holds schools of bait. In the spring and fall, this may be shallow, between 5 and 20 feet. Summer heat that warms surface temperatures to the high 50s or above will drive the mackinaw deep. In these conditions, deep humps in 100 to 200 feet of water can be hotspots for lakers. For deep-water fishing, a good fish finder becomes a key piece of equipment, though knowledge of the lake and a contour map can provide enough intel for finding the fish.