This module will include the description of the nature of lakes, rivers and catchment areas. The processes leading to formation of lakes, and lake morphometry will be covered. The vertical illumination of water bodies and extinction coefficient will be explained as well as the description of temperature stratification and its effects on the distribution of organisms. Roles of sediment in deep and shallow lakes, depth in the distribution of communities in a lake or river shall be discussed. The course shall also highlight lake fertility and hypolimnetic oxygen depletion. In addition, it will examine the diversity and functions of plankton, neuston, nekton, and benthos in freshwater ecosystems. Freshwater macrophytes and associated invertebrates, and weed-bed communities, e.g. epiphytic algae and bacteria will be studied.