As with all ecosystems, river systems involve a complex interaction of a rich diversity of microorganisms, plants and animals with their physical and chemical environment. Uniquely,the river habitat presents particular problems for organisms exposed to unidirectional currents, seasonal variation in flow, and disturbance due to pollution and other human interference. The book starts with a description of the taxa, their adaptations and their ecologies, followed by chapters describing the ecosystem processes in the terms of trophic interactions and the key production processes related to photosynthesis and decomposition. An important chapter considers the principles, practices and