This book water biology pertains to the aspects of the ecology of surface waters, including rivers and lakes, connected ground waters, flood plains and wetlands. It also focuses on the physico-chemical, biological and microbiological parameters of the water and wastewater. It helps to know about the quality and present status of water. It also deals with the structural and functional interrelationships of organisms of inland waters as they are affected by their dynamic physical, chemical, biotic environments and the impact of human activities on these systems. The book contains 29 chapters that are thoroughly reviewed by the authors and provides ample information on micro-organisms, algae, macrophytes, invertebrates, fish and other vertebrates, as well as those concerning whole systems and related physical and chemical aspects of the environment. Authors took much care in presenting the easiest way to understand the properties of water. The book will be of great help to the students of UG and PG, researchers, policy makers and stakeholders in the field of environment.