The article by James R. Karr, titled "Biological Integrity: A Long-Neglected Aspect of Water Resource Management," published in *Ecological Applications* in 1991, highlights the importance of biological integrity in water resource management. Karr argues that while water quality and quantity are critical, the biological aspects have been overlooked in favor of physical and chemical indicators. The "fishable and swimmable" goal of the 1972 Water Pollution Control Act and the need to restore and maintain biotic integrity underscore the biological underpinnings of water resource management. Karr identifies several factors contributing to the neglect of biological integrity, including the dominance of reductionist viewpoints, limited legal and regulatory programs, and the focus on point-source pollution control. He emphasizes the need for interdisciplinary approaches and ecological principles to address the complex issues affecting water resources. The article introduces the Index of Biotic Integrity (IBI), a tool developed to assess biological integrity in running waters. IBI uses a set of attributes that measure the organization and structure of fish communities, covering ecological levels from individuals to populations, communities, and ecosystems. The IBI is designed to be broadly based and ecologically sound, incorporating regional variations and natural biogeographic differences. Karr discusses the development and application of IBI, highlighting its advantages such as quantitativeness, reflection of biological systems, and systematic professional judgment. He provides examples of successful uses of IBI in various contexts, including the effects of mine drainage, sewage effluent, and habitat alteration. The article concludes by emphasizing the importance of expanded use of ecological expertise in ambient biological monitoring to protect water resources effectively.The article by James R. Karr, titled "Biological Integrity: A Long-Neglected Aspect of Water Resource Management," published in *Ecological Applications* in 1991, highlights the importance of biological integrity in water resource management. Karr argues that while water quality and quantity are critical, the biological aspects have been overlooked in favor of physical and chemical indicators. The "fishable and swimmable" goal of the 1972 Water Pollution Control Act and the need to restore and maintain biotic integrity underscore the biological underpinnings of water resource management. Karr identifies several factors contributing to the neglect of biological integrity, including the dominance of reductionist viewpoints, limited legal and regulatory programs, and the focus on point-source pollution control. He emphasizes the need for interdisciplinary approaches and ecological principles to address the complex issues affecting water resources. The article introduces the Index of Biotic Integrity (IBI), a tool developed to assess biological integrity in running waters. IBI uses a set of attributes that measure the organization and structure of fish communities, covering ecological levels from individuals to populations, communities, and ecosystems. The IBI is designed to be broadly based and ecologically sound, incorporating regional variations and natural biogeographic differences. Karr discusses the development and application of IBI, highlighting its advantages such as quantitativeness, reflection of biological systems, and systematic professional judgment. He provides examples of successful uses of IBI in various contexts, including the effects of mine drainage, sewage effluent, and habitat alteration. The article concludes by emphasizing the importance of expanded use of ecological expertise in ambient biological monitoring to protect water resources effectively.