The water column refers to the water in a lake or pond, exclusive of its bed or shoreline.

Composition

The water in a pond or lake may be fresh, salty, or alkaline; it may be clear or cloudy; it may be polluted or clean. What determines its characteristics are where it comes from and the nature of its bed or basin. For example, if a river flowing into a lake carries a large quantity of sediment with it, the water in the lake will be muddy.

Zones

Different parts of a lake or pond may have different features and support different kinds of plants and animals. These different parts are called zones. Zones may be determined by temperature, vegetation, or light penetration.

Zones determined by temperature Because they are relatively shallow, ponds and small lakes often have a uniform temperature throughout. The water in...