The Columbia River stands as the largest river system in the Pacific Northwest, draining a vast watershed that covers approximately 258,000 square miles, an area roughly the size of France. This massive basin extends through seven U.S. states—including Oregon, Washington, Idaho, and Montana—and into British Columbia, Canada. The river’s immense flow, the greatest of any river entering the Pacific Ocean from North or South America, carves out a diverse array of ecological niches. This varied environment supports a complex community of fish, which utilize the river for migration, spawning, and year-round residence.
The Anadromous Giants
The most iconic group of fish in the Columbia River are the anadromous species, those that hatch in fresh water, migrate to the ocean to mature, and return to their natal streams to reproduce. This group includes five species of Pacific salmon, the Steelhead trout, and the ancient Pacific Lamprey. Historically, the river once supported annual returns of salmon and Steelhead that may have exceeded 10 million fish, though modern returns are only a fraction of that number.
Chinook salmon, often called King salmon, are the largest of the Pacific salmon, known for spending between three and eight years in the ocean before their spawning migration. Coho salmon typically spend about 18 months at sea and are recognizable by the small black spots on their upper tail lobe. Sockeye salmon juveniles must rear in a lake for up to two years before migrating to the sea, making them dependent on specific lake and stream systems.
Chum and Pink salmon generally spend less time in freshwater as juveniles. Pink salmon have a fixed two-year life cycle and are the smallest of the Pacific salmon. Steelhead, the anadromous form of rainbow trout, are iteroparous, meaning they have the ability to survive spawning and return to the ocean to repeat the cycle. Pacific Lamprey, an ancient, jawless fish, shares this migratory life cycle. These migratory species serve as a crucial ecological link, transferring marine nutrients from the ocean back into the river’s headwaters when their bodies decompose after spawning.
Resident Native Species
In contrast to the ocean-going migrants, the Columbia River basin is home to native species that complete their entire life cycle exclusively within fresh water. The White Sturgeon is the largest and longest-lived freshwater fish in North America. Individuals can reach up to 19 feet in length and weigh over 1,800 pounds, with some documented specimens living for over a century.
White Sturgeon are bottom-dwellers, using their sensitive barbels to locate prey like crustaceans and small fish along the riverbed. They take a long time to reach maturity, with females typically not spawning until they are over 18 years old. This slow life history makes them susceptible to environmental changes, which is why the upper Columbia River population is currently listed as endangered.
The river system also supports native trout species, such as the Bull Trout and Redband Trout, which are sensitive to water temperature and habitat quality. Bull Trout are a char species that require cold, clean water for spawning and are known predators, feeding on smaller fish like Sculpin and Whitefish.
Other resident natives include several species of Suckers, like the Bridgelip Sucker, which graze on periphyton and invertebrates along the substrate. Various species of Sculpins, such as the Mottled Sculpin, inhabit the river bottom, where they feed on aquatic insects and serve as an important food source for larger native predators.
The Non-Native Invaders
The Columbia River’s fish community has been altered by the introduction of species that are not native to the Pacific Northwest. Many of these non-native species were intentionally introduced for sport fishing, while others arrived accidentally, and their expanding populations compete with or prey upon native fish. The warm-water habitat created by the river’s numerous dams and reservoirs provides ideal conditions for these introduced species to thrive.
Two prominent non-native sport fish are Smallmouth Bass and Walleye, both voracious predators. Smallmouth Bass have been documented consuming significant numbers of juvenile salmon and Steelhead as the young fish migrate downstream through the slow-moving reservoir sections of the river. Walleye, a large, predatory perch species, have been expanding their range upstream in the Columbia and Snake rivers, occupying areas that are crucial rearing and migratory corridors for juvenile salmonids. Their expansion is a concern for the recovery of protected native fish populations.
Other introduced species like the Common Carp and various Catfish species, including the Channel Catfish, also impact the native ecosystem. Common Carp are bottom-feeders whose rooting behavior can stir up sediment, reducing water clarity and damaging aquatic vegetation that serves as habitat for native species. Channel Catfish are generalist predators that, along with Walleye and Smallmouth Bass, contribute to the overall predation pressure on out-migrating juvenile salmon and Steelhead. The presence of these non-native species is often correlated with warmer water temperatures, suggesting that climate change will likely favor their continued expansion in the river basin.
Conservation Status and Protection Efforts
Columbia River native fish populations are struggling due to habitat loss, dam construction, and the resulting changes to the river’s flow and temperature. As a result, 13 distinct populations of salmon and Steelhead in the Columbia River Basin are listed for protection under the Endangered Species Act (ESA). The resident Bull Trout and the Kootenai River White Sturgeon are also listed under the ESA, reflecting the widespread impact of habitat degradation on the native fish community.
Protection and restoration efforts are multifaceted, focusing on mitigating the impact of the hydroelectric system. Measures include the operation of fish bypass systems to help juvenile migrants navigate dams and the implementation of water flow augmentation. Water flow augmentation involves releasing water from upstream reservoirs to aid in the downstream migration of smolts.
Restoration work also targets habitat improvements, such as ensuring better fish screens on irrigation diversions and restoring natural river flows and riparian areas. While hatcheries continue to produce millions of fish annually to supplement wild populations, these programs are a source of ongoing debate. Some conservation groups argue that they may harm the genetic integrity and recovery of the remaining wild salmon and Steelhead runs.