Yukon River

• Category: Inland Aquatic Biomes.
• Geographic Location: North America.
• Summary: The fifth-longest river in North America is being threatened by oil exploration.

The Yukon River is the fifth-longest river in North America and is considered to be the longest free-flowing river on the continent. Only one dam has been constructed on the river. Yukon, in the Gwich’in language, is from a Gwich’in phrase often translated as “white water river.” The Yukon River begins near Whitehorse, British Columbia, and flows for about 1,988 miles (3,200 kilometers) to the Yukon delta and the Bering Sea in Alaska. The Yukon River lies in the largest freshwater ecoregion in North America, which includes all but the southern portion of Alaska and several other rivers draining into the Bering and Beaufort seas. It spans northwestern Canada and central Alaska, draining more than 330,000 square miles (about 850,000 square kilometers).

Major rivers draining into the Yukon include the Teslin, Big Salmon, Nordenskiold, Pelly, White, Stewart, and Klondike. The Yukon basin is formed as the river flows through Alaska; the population of the entire Yukon River basin is about 126,000, mostly concentrated in Whitehorse on the upper Yukon River and Fairbanks, Alaska, on the lower stretch.

The Yukon basin lies in the continental climate zone, characterized by cool summers, cold winters, and low annual precipitation. The basin includes several terrestrial ecoregions: the Yukon Interior Dry Forests in the upper part, the Interior Yukon-Alaska Alpine Tundra in the middle basin, the Interior Alaska-Yukon Lowland Taiga in the northern part, and the Beringia Lowland Tundra in the lower part. The landscape of the basin is natural tundra and boreal forest.

The headwaters of the Yukon collect in the Teslin, Atlin, Tagish, and Bennett Lakes in the northwestern corner of British Columbia. From Whitehorse to Dawson City, the Yukon receives water from large tributaries. Then it flows into the Yukon Flats area, which is protected as the Yukon Flats National Wildlife Refuge. Flowing out of the flats, the river crosses the Trans-Alaskan Pipeline and flows west through the Nulato Hills along the west coast of Alaska. There, the Tanana, Innoko, and Koyukuk Rivers join the Yukon, forming the Yukon Delta. This delta is similar in topography to the Mississippi River Delta but is twice as large.

Like that of many northern rivers, the hydrology of the Yukon River is influenced by seasonal and annual variations in temperature and precipitation, and by their effects on the supply of glacial meltwater and the distribution of permafrost. The mean annual discharge of the Yukon is 223,895 cubic feet (6,340 cubic meters) per second, which is the sixth-largest in North America. Because of the cold environment, evapotranspiration is relatively low, and annual runoff is a high fraction of precipitation. The strong influence of temperature on runoff indicates that climate change will influence the overall function and seasonal dynamics in the future.

Flora and Fauna

Common trees in the Yukon River biome include white and black spruce, alpine fir, lodgepole pine, balsam poplar, white birch, and green alder in boreal forests; higher-elevation areas feature shrubs and sedges. The area holds rich floral diversity, with many species still being discovered. Wetlands and grasslands spread across great expanses between hilly zones.

Because of the extreme climate, the overall diversity of invertebrates is low in the Yukon basin. Few species of mollusks, clams, or snails have been reported. Diptera (true flies), mayflies, and stoneflies dominate the insect community in the basin.

Similarly, only thirty-eight fish species have been reported in the Yukon River. Two fish, the Arctic grayling and the Alaska blackfish, are considered to be the icons of the Yukon River. The Arctic grayling is found throughout the river, and the Alaska blackfish is common in weedy areas in the lower part of the river.

In addition, several ecologically and culturally important salmonids, lake trout, Dolly Varden, and Chinook salmon, are found in the Yukon River. Other notable fish species are the endemic (found only here) Arctic lamprey, as well as such regionally distributed types as wintering spawning burbot, Bering cisco, whitefish, chum salmon, coho salmon, northern pike, and rainbow trout.

Some of the keystone terrestrial fauna in the Yukon are bald eagles, beavers, muskrats, brown and black bears, and moose.

Effects of Human Activity

In the twentieth century, the Yukon River basin became part of a transportation route to the south for oil and gas. Hydrocarbon fuel exploration in Alaska began in the mid-1950s, before statehood in 1959. In the mid-1960s, a major oil discovery on the north slope of Alaska led to the construction in 1977 of the Trans-Alaskan Pipeline, which runs through the Yukon River basin. Additional oil exploration has been conducted on the northern slope of Alaska and in and around the Arctic National Wildlife Refuge. The ongoing gold mining and oil exploration activities of the region have directly affected the Yukon River basin.

Major effects include direct pollution of lower streams from mining activities, loss and fragmentation of wildlife habitat, disruption of water flow, and secondary ecological degradation from oil exploration and infrastructure. However, the effects can worsen further from mining, oil exploration, forestry, dams, and climate change. Climate change has significant effects on the hydrology and ecosystems of the river, as these are largely controlled by seasonal temperature regimes. Warmer temperatures can change the hydrological patterns regulated by autumn freezes and spring melts. In particular, climate change has led to increased ice jam floods, which damage surrounding areas and bring more contaminants into the river.

The effects of climate change have also had a negative impact on the Yukon River’s salmon population. According to NOAA Fisheries, in 2023, high-latitude rivers like the Yukon River were warming at twice the rate of other rivers. Warmer water makes it harder for their heart to pump oxygen. Their immune systems have been affected, and many have contracted the parasite Ichthyophonus, which can kill fish, according to a 2023 article on the Alaska Public Media's website. The Chinook salmon run in 2020 was considered so weak that it did not replenish the salmon population in the Canadian portion of the river. That year’s chum salmon run was also the lowest ever recorded. The low salmon populations prompted both Alaskan and Canadian authorities to halt both commercial and subsistence Chinook salmon fishing in the river in 2020 and chum salmon fishing in 2021. In April 2024, Alaska and Canada adopted a 2024–2030 management agreement that continued to direct most Chinook salmon subsistence fishing closures unless projected border passage exceeded a specified threshold.

The warmer temperatures are also thawing the region’s permafrost and increasing the release of mercury that is naturally found in the soil. A 2020 study published in the journal Nature Communications found that if the problem continues, mercury concentrations in the river will top the US Environmental Protection Agency’s mercury criterion by 2050.

Bibliography

“Agreement of April 1, 2024, Regarding Canadian-Origin Yukon River Chinook Salmon for 2024 Through 2030.” Alaska Department of Fish and Game, 2024, www.adfg.alaska.gov/static/home/news/hottopics/pdfs/yukon_river_chinook_salmon_7_year_management_2024_2030.pdf. Accessed 7 Mar. 2026.

Benke, Arthur C., and Colbert E. Cushing. Rivers of North America. Elsevier Academic Press, 2005.

"Changing Environmental Conditions on the Yukon River May Pose a Challenge for Juvenile Salmon." NOAA Fisheries, 20 Mar. 2023, www.fisheries.noaa.gov/feature-story/changing-environmental-conditions-yukon-river-may-pose-challenge-juvenile-salmon. Accessed 7 Mar. 2026.

"Effects of Climate Change on Arctic Rivers Monitored by Scientists." Innovation News Network, 10 Mar. 2023, www.innovationnewsnetwork.com/effects-climate-change-arctic-rivers-monitored-scientists/30876/. Accessed 7 Mar. 2026.

George, Kavitha. "Too Hot’ for Salmon: How Climate Change Is Contributing to the Yukon Salmon Collapse." Alaska Public Media, 26 Sept. 2023, alaskapublic.org/news/2023-09-26/too-hot-for-salmon-how-climate-change-is-contributing-to-the-yukon-salmon-collapse. Accessed 7 Mar. 2026.

“Mercury Concentrations in Yukon River Fish Could Surpass EPA Criterion by 2050.” National Snow and Ice Data Center, 16 Sept. 2020, nsidc.org/news-analyses/news-stories/mercury-concentrations-yukon-river-fish-could-surpass-epa-criterion-2050. Accessed 7 Mar. 2026.

Roland, Carl, et al. Results of an Inventory of Vascular Plants of Yukon-Charley Rivers National Preserve. Central Alaska Network, National Park Service, 2004.

Rosen, Yereth. "Yukon River, Beset by Salmon Woes and Mercury Threats, Signals Broader Arctic Climate Change." Arctic Today, 29 Sept. 2020, www.arctictoday.com/yukon-river-beset-by-salmon-woes-and-mercury-threats-signals-broader-arctic-climate-change/. Accessed 7 Mar. 2026.

“Yukon Climate Change Indicators and Key Findings 2015.” Northern Climate ExChange, 2016, www.yukoncollege.yk.ca/sites/default/files/inline-files/Indicator_Report_Final_web.pdf. Accessed 7 Mar. 2026.

"Yukon Freshwater Fishes." Government of Yukon, yukon.ca/sites/default/files/env/env-yukon-freshwater-fishes.pdf. Accessed 7 Mar. 2026.