A reservoir is a body of water impounded behind a dam on a river. When the dam is completed, water floods the terrestrial landscape, covering marshes, plains, forests, road beds—even houses and barns, in some cases. We classify reservoirs based on the topography of the terrain where the river is dammed, from deep canyon reservoirs to shallow lowland-wetland impoundments. Reservoirs in the North, West, and East produce cooler environments than those in the South, Southwest, and Southeast. Because crappies are on the cusp between coolwater and warmwater designations as a species, they thrive in all kinds of impoundments throughout the continent.

In general, impoundments make fantastic homes for crappies from Arizona to Maine. From low, swampy, flat regions to hill-land, and even in highland and canyon reservoirs, crappies seem well adapted to carving out a niche.

Reservoirs in these various landforms have the same basic configuration. Each is deepest by the dam and shallowest at the upstream end, so we divide the reservoir into thirds. The deepest water in each segment is always in the old river channel, unless it silts in. Wherever creeks flow into an area that’s impounded, a “creek arm” is created that wanders back between the hills. The confluence of an old creek channel with the old river channel within the impoundment is always a key spot for one species or another. The other end, or back end, of these creek arms and connecting coves becomes a critical spot for spawning crappies in spring.

Shape and depth of the pool and the surrounding topography determine how we categorize a reservoir. By studying a topographical map, you can usually determine what classification an impoundment falls into. Other facets of a reservoir’s personality include (1) annual fluctuation of water level, (2) overall water clarity, (3) fertility, and (4) temperature.

IMPOUNDMENT CLASSIFICATION

We use six broad categories to classify reservoirs: canyon, plateau, highland, hill-land, flatland, and lowland (or wetland). These classes are based on regional and geological aspects of North America’s wildly various landforms. Both natural and manmade characteristics determine what class an impoundment fits into. There are, of course, many exceptions. Some small reservoirs and “flowages” are hard to classify. Also, some reservoirs have portions characteristic of different classes, just as rivers and lakes do.

Lowland Impoundments

Lowland impoundments are the shallowest category of reservoir, sometimes with a maximum depth of fewer than 15 feet, usually found in the old creek channel. A small dam blocks a small river, causing a wetland to fill and spread greatly due to the low, flat terrain. In Wisconsin, lowland impoundments called flowages provide multispecies fisheries, as do lowland impoundments on bayous in Louisiana.

Lowland impoundments feature vast flats with cover provided by the flooded timber and thick vegetation that sometimes grows in rich soils. Some such waters have many small, low islands and may contain old pond dams in the basin, offering a bit of structure. Current is minimal and fishing patterns are typically similar to those in natural lakes.

Flatland Impoundments

Many of the nation’s most notable crappie fisheries fall into the flatland classification. Waters like Barkley Lake, Kentucky-Tennessee; Lake Seminole on the Georgia-Florida border; and Santee-Cooper in South Carolina offer a broad, shallow basin extending from a main river channel that meanders through farmland and low hills. Several broad arms define former tributary creeks that may run only during the rainy season.

Because of the shallow, fertile basin, aquatic plants may thrive in clear impoundments, sometimes covering 50 percent or even more of the surface area of the reservoir. Weed-fishing patterns predominate in these waters, though flooded timber, brushy banks, and stumps also offer cover for crappies, particularly in flatland impoundments that are murky and thus have little plant growth. River channel ledges in the 12- to 20-foot range also hold crappies. Bass are abundant, too, and other species including white bass, hybrid stripers, and catfish are also common. These older reservoirs continue to offer excellent fishing.

Hill-Land Impoundments

Hill-land impoundments provide the classic reservoir shape, with many small fingers branching from a main basin that surrounds a major river channel. These impoundments are deeper than flatland impoundments but not as wide, because hills on either side of the river constrict them. Creek arms are narrower and deeper, with extensive submerged timber, though this form of cover has been declining over the many decades since most of these reservoirs were built.

Water color ranges from fairly clear with a greenish tinge to stained. The color may vary seasonally, with spring rains making the water murky and summer plant growth fostering clear water in creek arms. The upper end of the reservoir tends to be murkier where the main river enters, with silt gradually falling out as water approaches the deep basin near the dam. Crappies often undertake seasonal shifts in location, particularly during the Prespawn and Postspawn Periods, and prior to the Coldwater Period.

Highland Impoundments

Dams on highland impoundments usually are constructed in steep, narrow ravines. This category of reservoir is therefore narrow but very deep, where high bluff walls border long, narrow, deep-creek channels. The basin itself is also narrow and extends from higher elevations down to the dam. The deep basin offers few or no islands, but tributary creek arms may include islands and underwater humps. Most crappie fishing in spring occurs in the upper end of creek arms as fish move from deep structure to spawning areas.

Clear water with little cover can be a challenge for anglers. Crappies may live in available shallow cover or hold in water deeper than most anglers are accustomed to fish. Preyfish are not abundant, which limits crappie numbers. Dawn, twilight, and night-fishing are popular on these waters, because crappies roam shallower and seem to feed more actively in low-light conditions.

Canyon Impoundments

Huge concrete dams across steep, narrow canyons form canyon impoundments, the dominant type in the Southwest and West. These waters are the most capacious and deepest reservoirs, often over 200 feet. They’re also ultraclear, a result of the sand and rock that form the basin. These substrates yield little plant life, so cover is in the form of sparse stick-ups, boulders, and sheer canyon walls with occasional rock slides. Canyon impoundments are narrow and very long, with long tributary arms.

These oligotrophic impoundments typically feature a deep, oxygenated hypolimnion that supports stocked rainbow trout. Warmwater species like crappies usually inhabit shallow bays and tributary arms, but also may roam the open water to feed.

Plateau Impoundments

In the high plains and low plateau regions from the Missouri River west to the eastern base of the Rockies, plateau impoundments prevail. These long, windswept reservoirs have a maximum depth in the 50- to 90-foot range. Though they may have long tributary arms, most coves are short and wide, not providing much protection from wind and waves. Due to wind, wave action, and loose substrate, vegetation is sparse. Plateau impoundments can offer good fishing in sections of the impoundment that contain hill-land or flatland characteristics. Where pelagic preyfish like shad, smelt, or alewives are found, crappies suspend consistently, except during the Spawn Period.