This research provides a comprehensive overview of the microscopic life forms found in water environments and how they are classified and function. These tiny organisms, including bacteria, archaea, fungi, algae, and viruses, play crucial roles in maintaining healthy aquatic ecosystems. The study shows how modern molecular techniques have revolutionized our understanding of these microorganisms and their relationships to each other. Impacts on everyday life: – These microorganisms help purify water by breaking down pollutants and organic matter – They form the base of aquatic food chains that support fish and other seafood we consume – Some of these organisms are used in wastewater treatment plants to clean sewage – Understanding these organisms helps in monitoring water quality and preventing waterborne diseases – Their study has led to important biotechnology applications, including the development of new medicines and industrial processes