West Dock Causeway was constructed in the Beaufort Sea, between Gwydyr Bay to the west and Prudhoe Bay to the east, to support oil exploration and to access a seawater treatment facility 2.5 miles (4.3 km) north of the mainland; about 59 miles (95 km) northeast of Nuiqsut and 15 miles (24 km) north of Deadhorse, Alaska. Prudhoe Bay was named in 1826 by the British explorer Sir John Franklin in honor of Algernon Percy, fourth Duke of Northumberland and Baron Prudhoe, of Prudhoe Castle in Northumberland, England. The bay is the principal settlement along the Beaufort Sea and the center of petroleum production on the coastal lowland known as the North Slope. The Trans-Alaska Pipeline System carries crude oil south from Prudhoe Bay to Valdez in Prince William Sound. Also named in 1826 by Franklin, the Beaufort Sea honors Sir Francis Beaufort, hydrographer to the British Admiralty. Four water masses characterize it: a cold surface layer; a warmer subsurface layer originating in the Bering Sea and Pacific; a deep layer of warm Atlantic water; and cold bottom water. Currents follow a clockwise Arctic Ocean gyre, flowing along the coast from east to west. The continental shelf is narrow and shallow, with many barrier islands and lagoons typically ice-covered except from August through September. The mainland is the Arctic Coastal Plain—low-lying, almost entirely permafrost-covered, and dotted with tundra and shallow lakes.

A major expansion in petroleum development at Prudhoe Bay occurred between 1973 and 1983, when the Trans-Alaska Pipeline was built and became operational. By 1983, offshore development had grown to include artificial gravel islands for exploratory drilling and the construction of West Dock to replace East Dock as the main port facility. Construction began in the winter of 1974–75, extending the causeway about 3,600 feet (1,100 m) north into the Beaufort Sea from the northwest shore of Prudhoe Bay. In its first year of operation, supply barges became trapped in sea ice about 4,800 feet (1,463 m) from shore, and emergency permits were granted to extend the causeway to a depth of 6–7 feet (2 m) at about 7,920 feet (2,414 m) from shore. Regulatory agencies grew concerned about the impact of solid-fill causeways on coastal circulation and the migration of fish and marine mammals. Studies assessing the causeway’s impact were initiated but proved inconclusive. In 1979, a further extension of 4,560 feet (1,389 m) to a water depth of 12 feet (3.6 m) was proposed, to accommodate a seawater intake and treatment plant for waterflooding—a secondary process used to extract oil from existing wells. Completed in 1981, this brought the total length to 13,200 feet (4,023 m), including a bridge spanning a 52-foot-wide (15.8 m) channel to allow passage for fish and small boats. The causeway was also widened to carry additional utilities, with a roadway 39 feet (12 m) wide and 18 feet (5.5 m) above mean sea level.

Waterflooding, or water injection, increases reservoir pressure to stimulate oil production. Water is injected both on- and offshore to push oil toward wells and maintain reservoir pressure; normally only 30% of oil in a reservoir can be extracted, but water injection raises that figure and sustains production over a longer period. In 1983, a large barge-mounted seawater treatment plant, designed to treat up to 2 million barrels of seawater per day, was permanently docked at the end of the causeway. Continued development of the Prudhoe Bay oil field and satellite reservoirs on the North Slope required the construction of two gravel causeways—the other at Endicott in the Sagavanirktok River delta. These solid-fill structures have caused measurable changes in nearshore hydrography, circulation, ice formation, upwelling and nearshore sediment transport, and have likely disrupted the migration of fish and marine mammals. Between 1985 and 1993, studies examined the causeways’ effects on the feeding and migratory patterns of least cisco and arctic cisco. In two of the four years when juvenile least cisco were abundant, catch rates were significantly lower east of West Dock, suggesting that small fish traveling west to east failed to bypass the causeway. A separate study found that humpback whitefish dispersing eastward from overwintering grounds in the Colville River had also been blocked. In response, a channel about 650 feet (200 m) wide was cut near the base of the causeway in the winter of 1995–96 to allow fish passage. Read more here and here. Explore more of West Dock and Prudhoe Bay here: