Coho Salmon spawn in the Tualatin River from late November to early December. Juvenile fish spend around a year in freshwater before migrating to the ocean as ”smolts”. After spending around a year and half in the ocean, adults migrate back to freshwater to spawn. After spawning, Coho Salmon die. Their dead bodies are an important source of food and nutrients for the river environment.
Coho Salmon did not migrate above Willamette Falls and enter the Tualatin River until the construction of the first Willamette Falls fish ladder in 1885. Hatchery stocking of Coho Salmon in the Upper Willamette River (includes the Tualatin River) started in the 1950s, but was discontinued in the 1970s. Coho Salmon were listed under the Endangered Species Act as threatened in 1998.
