Aquatic environments refer to the marine and aquatic ecosystems. They play a key role in maintaining the harmony between different ecosystems. The chapters included in this book provide a comprehensive understanding of this field with the help of topics such as microbial activity in underwater ecosystems, fresh water ecosystems, and physicochemical process in aquatic systems, etc. Researches and case studies compiled in this book are bound to provide an overview of the current advancements in the study of this field. It will help new researchers by foregrounding their knowledge in this branch.