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.