The Willamette River flows north through the heart of Oregon and supports a remarkably diverse aquatic ecosystem. The river basin is home to approximately 34 native fish species and an additional 28 to 33 introduced species. This collection includes massive, ancient species, small native forage fish, and popular sport fish introduced over the last century. The diversity of the fish population is categorized by their life cycles and origin, which determines their habitat use and ecological role.
The Critical Role of Migratory Fish
A large portion of the Willamette River’s native fish population is anadromous, migrating between the freshwater system and the Pacific Ocean. Their return migration transports nutrients from the ocean back into the river’s upper reaches, benefiting the entire ecosystem. The most prominent of these are the Pacific salmon and trout species, whose populations face ongoing management challenges.
The Upper Willamette River Spring Chinook Salmon and winter-run Steelhead Trout are both listed as Threatened under the federal Endangered Species Act (ESA). Populations of these salmonids have seen severe declines, largely due to 13 major dams in the Willamette basin that impede safe fish passage and alter natural water flows and temperatures. The Spring Chinook, the largest Pacific salmon species, typically returns from March to June, while the winter-run Steelhead is a prized catch for anglers.
Another anadromous species is the Pacific Lamprey, which is culturally important to Native American tribes. Adults return to fresh water after one to three years in the ocean, typically migrating upstream from May to July. Their larvae, called ammocoetes, burrow into sandy habitats for three to seven years, acting as filter feeders before migrating to the sea. The Willamette Falls fish ladder provides passage for these species, and the falls area is the site of the largest tribal harvest of lamprey in Oregon.
Resident Fish Species Endemic to the River
Many native fish species complete their entire life cycle within the freshwater confines of the Willamette River. These resident species are well-adapted to specific ecological niches, ranging from cool headwaters to the warmer, slower mainstem. This group includes resident Coastal Cutthroat Trout, which require clean, cool, well-aerated water to survive.
The White Sturgeon is a long-lived, bottom-dwelling species that can exceed ten feet and live for over 100 years. These fish use barbels near their mouths to sense food along the river bottom. Smaller native species, such as the Northern Pikeminnow, are common predatory fish, feeding on insects and smaller fish.
Largescale Suckers and various species of Dace occupy the role of forage fish and bottom feeders. The Largescale Sucker uses its ventral mouth to consume organic material from the substrate. These species are considered indicators of water quality and habitat health.
Established Non-Native and Introduced Species
The Willamette River’s fish community includes numerous introduced species that have established stable populations. These non-native species are often more tolerant of pollution and warmer water conditions, allowing them to thrive in the river’s lower and slower-moving sections. This group includes popular recreational fish like Smallmouth Bass and Largemouth Bass.
Smallmouth Bass are the most frequently encountered non-native fish in the lower Willamette River. Their predatory nature and expanding range have led to habitat overlap with vulnerable juvenile Chinook Salmon, posing a threat to native fish recovery efforts. These bass prefer areas with structure where they ambush prey.
The Channel Catfish is another introduced species, known for its forked tail and barbels. Walleye, a newer arrival in the upper Willamette system, are voracious predators due to their appetite for young salmon. The river also hosts the American Shad, an established anadromous species that completes its ocean-to-river migration annually.