This book provides the basic insights of “Limnology” in the Hindi language. It includes the introductory part of limnology, different ecosystems (Lake, River, Ponds, and Reservoir) and their biological productivity, Various planktonic organisms, aquatic plants, nektons, and benthos, and their distributions. All the physical, chemical, and biological phenomena occurring in the aquatic environment and their impacts were described with diagrams and suitable photographs.