This book addresses significant gaps in our understanding of how watershed microbial structures and functions respond to the pressures of urbanization. It consolidates rapidly evolving, yet often fragmented, global data on watershed microbiomes, providing critical insights into the impacts of urban pollution, human health risks, and long-term ecological consequences. Featuring the latest technological advancements in biological monitoring, microbial source-tracking technologies, and strategies for effective watershed management, this volume serves as a comprehensive and reliable source for the current state of urban watershed microbiology. It examines the unique challenges urbanization presents to ecosystems, especially in terms of atmospheric chemistry, hydrology, vegetation, and how these factors disrupt microbial communities that mediate essential ecosystem services like water purification, nutrient recycling, and degradation of pollutants. Together the two-volume work delves into the mechanisms behind the urban watershed syndrome?ecological degradation of streams?and explores many unanswered questions that hinder progress in understanding urban watershed microbiomes. With original research articles, reviews, and perspectives, this collection is a key resource for microbiologists, environmental scientists, engineers, and professionals involved in water quality, ecosystem management, and land-use planning. The hope is that this volume will inspire new breakthroughs, drive further research, and ultimately help shape effective strategies for addressing the ecological challenges of urban watersheds.