This book delves into maintaining adequate water flow within rivers and streams to protect aquatic ecosystems. It covers the legal, scientific, and policy aspects of instream flow management, exploring methods for determining appropriate flow levels and strategies for water allocation. Discussions include the ecological importance of instream flows for fish, wildlife, and riparian habitats. Case studies of successful instream flow protection efforts are analyzed, alongside the challenges of balancing water needs with environmental protection. A comprehensive overview for water resource managers, policymakers, and those interested in sustainable river management.