Structures and management strategies that enable fish to move past barriers such as dams, culverts, and weirs in rivers and streams. Fish passage is critical for maintaining migratory fish populations and aquatic ecosystem connectivity.
Fish passage refers to the ability of fish to move freely through river systems, and the engineered structures and management practices designed to facilitate that movement past human-made barriers. Barriers to fish migration include dams, road-stream crossings (culverts), weirs, tide gates, and other structures that block or impede both upstream and downstream movement. For anadromous species like salmon and steelhead that must migrate between the ocean and freshwater spawning habitat, barrier removal or fish passage facilities are essential for population survival. Common upstream passage structures include fish ladders (pool-and-weir, vertical slot, Denil types), fish elevators/lifts, nature-like fishways that mimic natural stream channels, and trap-and-transport systems. Downstream passage for juvenile fish past hydroelectric dams involves fish screens, bypass systems, spillway passage, and in some cases, barge transportation. The effectiveness of fish passage facilities varies greatly depending on the target species, structure design, hydraulic conditions, and maintenance. In the United States, over 90,000 dams and millions of culverts fragment river networks; prioritizing which barriers to address requires systematic assessment of connectivity value, species presence, and feasibility. Dam removal has emerged as the most effective fish passage solution, with major removals on the Elwha River (Washington) and Klamath River (California/Oregon) demonstrating dramatic ecological recovery.