The Yukon Delta, properly the Yukon–Kuskokwim Delta, is the vast tundra wetland in western Alaska, USA, where the Yukon River (3,190 km) and the Kuskokwim River (1,130 km) reach the Bering Sea. At roughly 129,500 km², about the size of Louisiana, it is one of the largest river deltas in the world: a flat coastal plain in an ecoregion where lakes and ponds cover almost a quarter of the ground and the outer wetlands sit so close to sea level that Bering Sea tides often flood them. Most of it lies within the Yukon Delta National Wildlife Refuge, about 77,500 km² (19.16 million acres), created on 2 December 1980 under the Alaska National Interest Lands Conservation Act from refuge lands first set aside by Theodore Roosevelt in 1909. It is also home to about 25,000 people, roughly 85% of them Yup’ik and Athabaskan Alaska Natives, in villages linked by bush plane, riverboat and snowmachine rather than roads. More than a million ducks and half a million geese breed on the refuge each year, so the clearest way to describe the delta is through the animals that depend on it.
Emperor geese on the Bering Sea fringe: 90% of the world’s nests
No bird is more closely tied to the delta than the emperor goose, a small, silver-grey goose with a white head that breeds only around the Bering Sea in Alaska and the Russian Far East. About 90% of all emperor geese nest on the Yukon–Kuskokwim Delta, and they nest close to the sea: their nests are built in coastal marshes no more than about 16 km from the shore. In Alaska the breeding season generally begins between 20 May and 3 June, a few weeks earlier than in Russia. The eggs hatch in late June and early July, and the goslings can walk, swim and feed themselves within hours.
The goose is also a migrant of short range. Instead of flying thousands of kilometres south, it moves only about 600 to 760 km to winter on ice-free mudflats and rocky shores, mostly in the Aleutian Islands, on the Alaska Peninsula and around Kodiak Island. Birds that fail to breed leave the delta in summer to moult on St. Lawrence Island or the Chukchi Peninsula.
The species’ history on the delta is a record of decline and partial recovery. The naturalist Edward William Nelson found emperor geese abundant on the Yukon–Kuskokwim Delta in 1879. By 1923 Arthur Cleveland Bent reported far fewer, blaming in part the heavy shooting of birds and taking of eggs. Counts give a clearer picture from the 1960s: about 139,000 birds in 1964, falling to 42,000 by 1986, then recovering to about 85,000 in 2002 and more than 98,000 in 2015. The IUCN still lists the goose as near threatened and describes the overall trend as decreasing.
Black brant and tundra swans in the coastal meadows
The emperor goose shares the delta’s salt marshes and tidal meadows with the black brant, the dark Pacific form of the brant goose. The account of the Beringia lowland tundra, the ecoregion that includes the delta, credits the delta with about half of the world’s black brant. The whole population, which breeds across north-western Canada, Alaska and eastern Siberia, numbers about 125,000 birds. It has swung widely within living memory, from about 200,000 in 1981 to about 100,000 in 1987. After breeding, most black brant winter along the Pacific coast of North America from southern Alaska to California, and some in East Asia.
Inland from the coast the flat tundra is broken by thousands of lakes and ponds, and here the larger waterbirds take over. The same ecoregion account describes the delta as home to the world’s largest communities of tundra swans, and the refuge records very large seasonal gatherings of northern pintail, loons, grebes and cranes. Eiders and harlequin ducks are among its breeding ducks too.
The water feeding all those lakes comes from two very different rivers. The Yukon, with an average flow of about 6,400 to 7,000 m³ per second, drains 854,700 km² of Alaska, Yukon and British Columbia. The Kuskokwim is shorter but is the longest free-flowing river in the United States and the longest river system contained entirely within one state. People depend on the wetlands as much as the birds do. Most residents still live a subsistence life of hunting, fishing and gathering, and more than 30% have cash incomes well below the federal poverty line.
Bristle-thighed curlews above the lower Yukon, found nesting in 1948
Some of the delta’s birds are long-distance champions. The bristle-thighed curlew, a medium-sized shorebird with a down-curved bill, was described in 1789 from a Tahitian specimen supplied by Joseph Banks, who had sailed with James Cook, yet its breeding grounds stayed unknown until 1948. They turned out to be in western Alaska: the birds nest on low-lying tundra on the lower Yukon River and on the Seward Peninsula, and nowhere else.
The curlew’s migration begins with a long ocean crossing. Adults leave their chicks at about five weeks old and head south first; the young follow once they have fattened up. The first leg is a non-stop flight of about 4,000 km from Alaska to Laysan in the north-western Hawaiian Islands, and the birds can fly more than 6,000 km without stopping. They winter on islands across tropical Oceania, from Micronesia and Fiji to Tuvalu, Tonga, Samoa and French Polynesia, where introduced predators and coastal development are a concern.
North of the lower Yukon the refuge also includes the Andreafsky Wilderness, about 5,300 km² designated by Congress in 1980. The Andreafsky River and its East Fork flow south-west along parallel paths and drain into the Yukon. Parts of the refuge have a longer conservation history than the 1980 consolidation: the Clarence Rhode National Wildlife Range had already been designated a National Natural Landmark in 1968.
Chinook salmon past Emmonak and Pilot Station: 58,500 counted in 2023
The delta’s rivers carry one of the longest salmon runs in the world. Chinook, coho and chum salmon all return up the Yukon to spawn, and the chinook have the longest journey: arriving at the river mouth in early June, some travel as much as about 3,200 km upstream, and an estimated 35 to 50% are bound for Canada. Because salmon do not feed on their way upriver, they enter the Yukon with great reserves of fat, which is why chinook from this river are prized.
The fish enter through the delta’s maze of channels. Below Mountain Village the main Yukon channel frays into many branches at the head of passes, and the villages of Nunam Iqua, Alakanuk, Emmonak and Kotlik sit on the delta channels; Emmonak, with about 760 people in 2000, is the largest and its gravel airstrip is a regional hub. Upstream, the river’s flow is measured at Pilot Station, about 121 miles (195 km) above the mouth. On the Kuskokwim side, Bethel, about 80 km upstream from Kuskokwim Bay, is the delta’s main town and service hub, with 6,325 people at the 2020 census.
The runs have been sharply reduced again and again. Low returns in the late 1980s, 1990s and 2000s led to a federal fishery disaster declaration for the 2008 and 2009 Yukon commercial chinook seasons. In 2010 the Alaska Board of Fisheries imposed the river’s first limit on net mesh size, 7.5 inches (190 mm), and in 2021 the state banned all chinook and chum fishing, subsistence fishing included. In the summer of 2023 the U.S. Fish and Wildlife Service counted 58,500 chinook, the second-lowest season on record. The causes are still debated, from ocean conditions and disease to bycatch in the Bering Sea pollock fishery. Since March 2001 the Yukon River Salmon Agreement between the United States and Canada has managed the shared run through a 12-member Yukon River Panel.
Muskoxen on Nunivak Island since 1935
About 48 km off the delta coast lies Nunivak Island, a permafrost-covered volcanic island of about 4,227 km², the second-largest island in the Bering Sea, most of it within the refuge. Its single settlement, Mekoryuk on the north shore, had 191 people in 2010. Nunivak once had a modest herd of caribou, but they were exterminated after firearms arrived in the late 19th and early 20th centuries.
Alaska’s native muskoxen had been wiped out by the late 19th or early 20th century. In 1935 the U.S. Fish and Wildlife Service brought muskoxen to Nunivak to support subsistence living, and reindeer followed in the 1930s and 1940s. Both herds are now maintained by Mekoryuk’s Native corporation. The muskoxen are valued for qiviut, the fine underwool collected after the animals shed in spring and spun into yarn that can sell for about $100 a skein. The Nunivak herd later became a source for other restorations: animals from Nunivak and Canada’s Banks Island were released on Russia’s Taymyr Peninsula in 1974 and 1975, and Nunivak animals on Wrangel Island in 1975, where there were about 1,100 by 2019.
For the river behind all of this, from its headwaters in British Columbia to the delta, read our Yukon River guide; to see where the delta’s geese and curlews fit into the world’s great migration routes, our guide to bird flyways; and for the rest of the state’s landscapes, Alaska’s geography.