Occasionally in mid-summer, walleyes will set up housekeeping along vast stretches of deep shoreline edges that break to very deep water. I ran into this scenario a few years back on North Dakota’s Lake Sakakawea while pre-fishing for a national tournament. I ended up winning that contest by fishing fish no one else believed were catchable. These were walleyes that were relating to deep main-lake flats. To target these fish, you’ll want to fish along the outside edges of deep water flats where the depths run (for example) from about the 30 ft range, then break sharply to as deep as 100 feet. The fish will usually be scattered along the edges of these large, deep flats so you’ll want to troll crankbaits to cover lots of water and get your baits in front of as many fish as possible.
Concentrate on looking for suspended walleyes relating to the sharp breakline. You won’t actually be fishing the structure itself, but rather the open water immediately adjacent to the flats edges. This is what we often refer to as “The Fringe” where walleyes pull off the structure at about the same depth as the edge, and feed on schools of bait relating to the structure. It takes practice locating these types of scenarios, but it’s very common in large reservoirs throughout walleye country.