Lowland-wetland and flatland impoundments are common in the northern and central Midwest. The deepest water is typically 18 to 40 feet near the dam. The rest of the reservoir is often one huge 10- to 15-foot flat divided by a meandering creek or river channel. It can be flooded wood, farm, or pasture land, swamp, or open prairie. The only structure is the original channel and a few nondescript humps. Main attractions include the riprap near the dam, scattered rock piles, usually left by farmers, and perhaps a flooded woodlot that may now be no more than a stumpfield.

Flatland impoundments—Flatland reservoirs are constructed in agricultural or low wooded areas and may or may not have significant siltation, depending on the surrounding landform. Feeder creeks and rivers draining farm fields or cattle farms typically offer walleyes poor spawning conditions because of siltation. Impoundments surrounded by woodlands or those with major feeder rivers may offer suitable rock structure in upriver sections to draw an upstream movement of fish in spring. In chains of reservoirs along major rivers, walleyes move miles upstream to the base of the next upriver dam, spawning on rocky shorelines or riprap before returning downstream.

If natural spawning conditions aren’t present in feeder rivers, look for rocky points in the main lake or rock and boulder faces of dams and causeways. Earthen dams covered with boulders often provide good spawning conditions.

Distinctive river channels in flatland impoundments twist and turn across shallow flats. Postspawn walleyes generally remain shallow, relating to the tops of flats with weed- or woodcover, or along the channel lip. If the water is clear or cover is lacking, walleyes may move toward the base of the channel, relating to outside bends. In general, however, these impoundments have dingy water, and food sources tend to be shallow in spring and summer. Only in fall and winter do walleyes tend to drop into the deepest available water.

Lowland-wetland impoundments—These reservoirs are located in swampy terrain. They often lack significant rock structure or rocky feeder streams. Many are bowl-shaped or have wide open, flat, soft basins. River channels are silted in except in lower ends near dams. Flooded shoreline weeds and wood, floating bogs, shallow submergent and emergent vegetation, and scattered woodcover on shallow flats break up the otherwise featureless terrain.

The prime spawning habitat can be upstream in the main river, especially in reservoirs not cleared of timber. Much depends on the river, however. If it has ample current, is relatively free of silt, and offers optimum spawning substrate (pea gravel), some walleyes may spawn there. Otherwise, fish will spawn along the riprap of dams and causeways, then disperse into the warming lake once spawning is complete.

Lowland-wetland walleyes seldom grow huge, but a 10-pounder is possible, and overlooked 3- to 4-pound fish are fairly typical. Flatland impoundments tend to grow slightly larger fish, though viewed as a whole, anglers equate the shallow, featureless lake scene with eatin’-sized walleyes rather than with trophies.

Reading not-so-classic Structure

Lowland and flatland reservoirs are the equivalent of eutrophic natural lakes. Both are shallow and fertile and usually have stained to dark water, which keeps walleyes relatively shallow most of the year. Lowland impoundments often have expansive dishpan-like soft basins in which the river channel has become silted up by erosion, except perhaps in the deeper portions near dams. Many have shallow shoreline weedgrowth and remnant timber or cut stumps on the flats.

Flatland impoundments feature extensive flats, with or without woodcover, and generally have distinctive river and creek channels cutting across them. These channels offer deep water fall and wintering areas, particularly at channel bends and intersections. Channels also serve as fish highways between shallows and deeper water. Both flatland and lowland impoundments tend to be wide, with wide cove mouths. River channels, where present, tend to lie far from shore, rather than brushing up against shoreline structure.

Cover often plays an integral role in both environments. Generally, stable water levels are conducive to developing weedgrowth, but dark water restricts it to the shallows, perhaps in bays.

In summer, walleyes may lie in cover atop flats adjacent to deep water or to creek channels. Walleyes tend to settle on favorable depth ranges based on water clarity, and they’ll make best use of any available cover at that level. Thus they can be some distance away from any obvious drop-off as long as the local conditions fulfill their needs for forage and safety.

Pitching to weed- or woodcover with jigs or slipbobber rigs or casting crankbaits atop the flats may outproduce rigging or jigging along channel edges—if channels exist. Suspended fish often feed on shad in midlake, particularly in waters where cover is absent, such as in the shallow impoundments of the central prairies or Ohio farm country. The most effective summer tactic may simply be to troll crankbaits with planer boards in areas where you see fish on your electronics.

Subtleties rather than obvious structure often dictate walleye location in these waters. Submerged woodcover ranging from a prominent field of standing timber or a tangle of logs deposited by current, down to an almost imperceptible scattering of sticks and limbs in a general area, may be sufficient to hold walleyes.

Slow tapers, except where creek or river channels are present, are the rule. These lakes can be a structure fisherman’s nightmare; at first glance, everything appears the same. Yet once you know what to look for, fish-attracting subtleties become more apparent.