David Walker studies ecosystem structure and function with a focus on how long-term and chronic exposure of anthropogenic organic compounds might shape populations and assemblages of organisms. He teaches stream ecology and works with Arizona Department of Environmental Quality on several issues, including aquatic ecosystem assessments and methodology. He also works on eco-flows from reservoirs, with the U.S. Fish and Wildlife Service on the Lower Colorado River multi-species management plan, and with USFWS and the U.S. Bureau of Reclamation on habitat creation for native fish species. He has worked with most municipalities in the state on limnological aspects of reservoirs used for drinking water and/or issues regarding effluent-dominated streams.