The substratum or floor of a water body may be rocky, sandy or muddy. It may also be flay, sloping, undulating, winding or weddy. Such water body may be river, stream, spring, pond, lake, sea or ocean. The nature of the substratum affects both the distribution and the type of organisms found in the aquatic habitat. In general, a muddy floor has more organic content than a sandy or rocky floor. As a result more organism live in a muddy substratum than in sand or rocky one, provided that the oxygen supply is sufficient in the former. Burrowing animals such ad mudskippers, crabs, worms and micro organisms are found in muddy and sandy substrata. Speed of flow of water is more in slopping and rocky floors. Hydrophytes (water plants) possess adaptive structures for attaching to rocks or water weeds, e.g. sponges and eggs of amphibians held in a chain of jelly. Depressions on undulating floors provide hideout either for breeding or for escape from predators among some aquatic animals such as fishes. Ponds or lakes may have water weeds on their floors, having a lot of organic matter. Such substrata provide good habitat for micro organisms, algae, amphibians and fishes.
