Chinook are the largest species of salmon, with adults often exceeding 40 pounds. As such, they tend to spawn in larger streams than other species of Pacific salmon. Juvenile Chinook spend from 3 months to 2 years in freshwater and then remain at sea for anywhere from 1-6 years, though on average, usually between 2-4 years.
Spring Chinook (or stream-type Chinook) tend to migrate to headwater streams of large river systems. They have a longer freshwater residency, and thus are more dependent on freshwater habitats. Fall Chinook (or ocean-type Chinook) are most often found in coastal streams and tend to migrate to salt water at a younger age.
There are eight evolutionarily significant units (ESUs) for Chinook salmon that fall at least partially in Oregon: the Oregon Coast, the Snake River Fall run, the Snake River Spring/Summer run, the Lower Columbia River, the Mid-Columbia Spring run, the Upper Willamette River, the Southern Oregon/Northern California Coast, and the Upper Klamath and Trinity Rivers.
Data for Lower Columbia River, Upper Willamette River, and Snake River Chinook are currently available on this site.