It varries from lake to lake, I tend to look more for bottom structure than depth, A sharp drop off, a plateua that sits several feet of the bottom ect. Most of the time I fish right off bottom, but have seen them caught all through the water colum to right up under the ice depending on where the smelts are schooling, but later in the year come march they tend to run up into the shallow water chasing smelt and other bait fish at least here in maine