The Copper River Delta is a wetland of tidal mudflats, sloughs, sedge marsh, ponds and sandbars on the Gulf of Alaska in southcentral Alaska, United States, where the 470 km (290 mi) Copper River fans out southeast of the town of Cordova. It covers about 700,000 acres (2,800 km²), spreads nearly 80 km (50 mi) along the coast, and is the largest continuous wetland on the Pacific coast of North America. Each year an estimated 16 million shorebirds use it, including what is thought to be the world’s entire population of western sandpipers. Much of it lies inside the Chugach National Forest, created in 1907, where delta lands make up about 31 per cent of the forest’s area, and it is the largest continuous part of the Western Hemisphere Shorebird Reserve Network. That protection has been tested by copper mining, an oil boom, the 1964 earthquake, the 1989 Exxon Valdez spill and a road that was never finished, and each of those threats is a dated part of the delta’s story.
1907: the Chugach National Forest draws a line around the delta
The delta’s first protection came early. A forest reserve was declared in the region in 1892, and in 1907 part of it became the Chugach National Forest. At 6,908,540 acres (27,958 km²) it is now the second-largest national forest in the United States and the northernmost and westernmost. It spans Prince William Sound, the eastern Kenai Peninsula and the delta, and roughly 30 per cent of it is ice. The Forest Service manages it for fishing, tourism and wildlife rather than timber: under 2 per cent of the forest is considered suitable for commercial logging, and it has only about 140 km (90 mi) of Forest Service roads. The Alaska National Interest Lands Conservation Act of 1980 later added 3.35 million acres to the Tongass and Chugach national forests together.
Being inside a national forest does not mean the delta is untouched. National forests allow mining, oil and gas work, and the Chugach has some of each. What has protected the delta in practice is its remoteness. Cordova, with 2,609 people in 2020, has no road link to any other Alaskan town except the nearby Eyak village, so people and goods arrive by ferry or plane.
1898 to 1938: copper, coal and Alaska’s first oil field
The first big industrial pressure came from the river’s name. Copper deposits on the upper river had long been worked by Alaska Native people, and the Kennecott mine was found in 1898. To move its ore, Michael James Heney built the Copper River and Northwestern Railway from Cordova between 1906 and 1911, crossing the delta on a line of bridges. The most important, the Miles Glacier Bridge, cost $1.4 million and became known as the Million Dollar Bridge; it carries the line over 460 m (1,500 ft) of the Copper River between Childs Glacier and Miles Glacier.
East of the delta, Katalla was the site of the first discovery of commercial quantities of oil in Alaska, in 1902, and it was meant to be the railway’s port for both copper and the Bering River coal fields. Storms in the autumn of 1907 wrecked the jetty being built there, and the terminus moved to Cordova. Katalla’s small oil field kept going until a fire on 25 December 1933 damaged its refinery, and the town was abandoned in the 1940s. The mine closed in 1938 and the railway shut down the same year. The delta escaped becoming an industrial corridor largely because the ore ran out. A Korean consortium explored the Bering River coal fields again in the early 1980s, but the coal did not look economic and any haul route would have crossed unstable slopes and areas hit by glacial outburst floods from Bering Lake.
27 March 1964: the earthquake that lifted the marshes
The biggest change to the delta in the past century was natural. On 27 March 1964 a magnitude 9.2 megathrust earthquake ruptured beneath Prince William Sound, the most powerful ever recorded in North America. Uplift spread across about 520,000 km² from Kodiak to the east of the sound, and around Cordova the ground rose by as much as about 1.8 m (6 ft). On the delta itself, the rise of roughly 1.2 m (4 ft) lifted tidal marsh out of reach of the tides.
The effects ran through the food chain. Cordova had called itself the “Razor Clam Capital of the World” from 1916, with harvests of up to 3.5 million pounds; the beds were already declining after a die-off in 1958, and the uplift, which left them exposed, effectively finished the industry. Drier wetlands let shrubs and predators move in, and nesting success fell for the dusky Canada goose, a dark subspecies whose breeding range is almost entirely the delta plus Middleton Island. Its population, about 20,000 to 25,000 in the 1970s, had fallen to between 12,000 and 15,000 by the 1990s. The quake also knocked span 4 of the Million Dollar Bridge off its pier and destroyed other bridges along the old railway line.
24 March 1989: Exxon Valdez oil and the Cordova fleet
Shortly after midnight on 24 March 1989 the tanker Exxon Valdez struck Bligh Reef in Prince William Sound and spilled about 10.8 million US gallons of crude oil. The oil eventually reached about 2,100 km (1,300 mi) of coastline, killing between 100,000 and 250,000 seabirds, at least 2,800 sea otters and an unknown number of salmon and herring. The spill hit Cordova, northwest of the delta, through its fishing economy rather than its marshes. Commercial fishing is the town’s main industry, and half of all households have at least one person who fishes or processes fish. Damaged salmon and herring stocks pushed the town into a local recession. The North American Pacific herring fishery as a whole, long overfished, collapsed in 1993. Litigation over the spill ran for years before about $450 million in compensatory and punitive damages was awarded.
The fleet that depends on the delta is large for a town of 2,609 people. In 2009, permits fished in the Prince William Sound and Copper River Delta area included 511 drift gillnet permits, 159 purse seine permits and 27 set gillnet permits. Drift gillnetters work the river mouth for the Copper River salmon runs, more than 2 million fish a year, which begin with chinook in May.
1945 to 2011: the Copper River Highway that stops at mile 36
A road across the delta was planned for decades. Construction of the Copper River Highway began in 1945 along the old railway bed, meant to link Cordova with the state highway system at Chitina, and the Million Dollar Bridge was converted for cars in 1958. The 1964 earthquake halted construction just beyond the bridge, and permanent repairs to the bridge were not finished until 2005. Then the river itself took over: in 2011 erosion washed out the approach to Bridge 339, and since then vehicles can reach only mile 36 of the 49.5-mile (79.7 km) road. The last 13.5 miles, and the bridge, can be reached only by boat.
The unfinished road is one reason the delta still works as a wetland. A link to Chitina would have opened the interior delta to traffic and development. Instead the paved section ends about 19 km (12 mi) from Cordova, gravel continues past Alaganik Slough and Pipeline Lakes, and the Copper River keeps moving its channels across the old railway line.
1950s to 2011: counting swans, geese and sandpipers
Much of the delta’s modern protection grew out of wildlife counts. In the early 20th century trumpeter swans were close to extinction, with fewer than 70 wild birds known in 1933. Aerial surveys in the 1950s found several thousand around the Copper River, and that Pacific population supplied birds for reintroductions that helped the North American wild population pass 46,000 by 2010. The delta is now described as having the world’s largest nesting population of trumpeter swans.
The Western Hemisphere Shorebird Reserve Network, launched in 1985, recognised the delta’s importance for migrating shorebirds, among them western sandpipers, least sandpipers and dunlin. Since 1984 the Forest Service’s Cordova Ranger District has run a dusky Canada goose programme with Alaska and Oregon wildlife agencies and Ducks Unlimited. It installed artificial nest islands in delta ponds to put nests out of reach of brown bears, coyotes and bald eagles; studies suggest eagles alone account for nearly 80 per cent of nest predation. Between 1984 and 2011, occupancy of those islands rose from 10 to 50 per cent, and nest success averaged 63 per cent a year. Cordova marks the spring migration with the Copper River Delta Shorebird Festival every May.
Glaciers, sediment and the delta’s next century
The delta is made of glacial silt carried down from the Wrangell and Chugach mountains, so its future depends on ice. Childs Glacier and Miles Glacier calve straight into the river, and the floodplain is lined with sand dunes up to 76 m (250 ft) high, built from silt blown off the river bars. Glaciers along the Alaskan coast are mostly retreating; to the east, the Bering Glacier has pulled back by up to 12 km since 1900. That changes the amount of water and silt reaching the delta, but how much is still being measured, through the Miles Lake sonar station, the Native Village of Eyak research stations and Alaska Department of Fish and Game salmon counts.
Those measurements matter because the threats to the delta have never come one at a time. The same delta that was lifted in 1964, oiled offshore in 1989 and almost crossed by a road is still Eyak homeland, a salmon fishery and a shorebird stopover. For a wider view of the state, see our Alaska geography guide, and compare it with the Fraser River Delta, another Pacific coast stopover for western sandpipers.