Flats Walleyes: Making a 3-D Map Rendering

In the March/April issue of In-Fisherman magazine, contributor David Harrison writes about tactics for shallow-water walleyes. One topic he focuses on in that article is locating walleyes on shallow flats, which are often considered featureless expanses. He discusses, however, how a 3-D rendering of a shallow flat, showing subtle depth changes, bottom features, and cover elements, can an important key to pinpointing walleyes.

Harrison: Using today’s electronics to map a shallow flat pays off by helping the angler understand the subtle changes that fish use to hunt and travel. Watching for these micro differences with a traditional sonar is futile, but a 3-D rendering of the area really pops. If done well, a huge flat suddenly becomes an area worth tossing jigs for a few minutes or for making strategically planned trolling passes, instead of a half-day exploration effort. Here’s how to make a 3-D rendering:

Start recording while using side-imaging sonar to look for activity, then use those data to make a 3-D rendering.

This isn’t traditional criss-cross mapping. Troll around or search with side-imaging while recording. After a few passes, you’ll have enough data to cover the details. This area is approximately half a mile long and shallow water (2 to 6 feet deep) extends 200 to 300 yards from shore.

Side-imaging clearly shows small rockpiles and logs in the otherwise barren flat. Mark features with waypoints to target with jigs or to simply avoid snagging lures while trolling. Add waypoints real-time on the water or at home.

At home, software like Humminbird Autochart Pro shows the “flat” in 3D, highlighting multiple small cups, drops, and ridges that can be targeted the next day with an optimized trolling path or location-focused jigging. Even without perfect coverage, the flat is no longer “flat.”

This expansive half-mile-long shallow water (0 to 6 feet deep) point at another lake has multiple hollows and spines that don’t necessarily show up on the contour map of the area. The extensive area in red, which is 4 feet deep or less, can be intimidating, but highly productive if worked efficiently.

This complex point, which takes about 15 minutes to troll from end-to-end, has sharp drops from 5 feet deep into 20 feet. Shown in bottom-hardness mode, this area is 100 percent soft mud and silt. The diamond on the left shows a mini-ridge close to the point that often holds fish. The divot marked by the circle in the middle of the map doesn’t show up on contour maps, and the secondary shelf on the front right marked by the triangle is another hidden spot. Each of these areas are small enough to cast to or fish with slipfloats while others troll the area. The largest part of the flat in the back right has a mini-point and small break in 3 feet of water marked by the star that is otherwise invisible on the water but with the right wind, should hold large walleyes. Trolling this area with crankbaits or livebait would, after a few fish, reveal their location, but knowing the details of features can reduce search time.

This mile-long shoreline area combines a flat with classic walleye structure. The red areas are less than 5 feet deep and surprisingly have few micro-details compared to the other areas. The long ridge at the bottom, the thumb in the middle, and the three features at the top that reach into 30 feet make this area a spot where walleyes can live year-round. Knowing the flat section is non-descript makes it easy to set up planer boards to cover water if fish aren’t deep or on the structure.

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This immense flat stretches around two main-lake points. Six feet of water far from shore eventually drops into 20. One day when the wind was blowing, enough fish were using the cup area and I had consistent action there on slipfloats while other boats trolled randomly. Another day, walleyes were up top and activity was visible on side-imaging so we used planer boards to cover the flat in one pass. The dark red areas near the shoreline would be good spots to anchor in higher winds.

This area shows an ultra-shallow flat and point. The red colors indicate bottom hardness highlighting some rocks at the back, the hard-bottomed channel, and a few small areas near the drop-off that should attract fish to this otherwise barren area.

“Draining” lakes with these maps helps anglers understand specific spots and predict areas that are advantageous in specific wind directions and conditions. The mental picture aligned with multiple presentation options helps anglers make decisions faster and spend less time between bites.