Benthos consists of all those aquatic organisms which are associated in some way with the bottom sediments. We shall, therefore, consider here only the organisms and communities inhabiting the lake sediments, reserving a study of the periphyton found on higher aquatic plants for a further chapter. This periphyton was far from negligible in Lake Chad where fringing vegetation and submerged water grasses were numerous. It was usually composed of different species to the benthos although some were occasionally found among the benthos when it was sampled close to plant clumps.