Function and watershed‐based stream mitigation: Lessons from a program development and implementation odyssey in the Western United States

Abstract To improve the quality and success of compensatory mitigation under Clean Water Act Section 404, the U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency jointly promulgated regulations in 2008. These regulations promote the use of function assessments to determine appropriate compensatory mitigation to replace functions and services lost due to permitted impacts to aquatic resources and require a watershed approach to mitigation. The Oregon Removal‐Fill law, administered by the Department of State Lands, has similar requirements. Despite higher level policy, there is a paucity of scientific focus at the practical level needed to improve the tools and practices required for regulatory program implementation to achieve better mitigation outcomes, contributing to an implementation gap. By describing key challenges and specific solutions, we share lessons from a 15‐year interagency effort to develop and implement an integrated, function, and watershed‐based stream compensatory mitigation program in Oregon. We highlight the importance of an intentional process of engagement and change management and identify outstanding science and policy needs to improve stream compensatory mitigation programs and field‐scale outcomes.