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.