The Pacific geoduck (/ˈɡuːiˌdʌk/ GOO-ee-duk; Panopea generosa) is a species of very large saltwater clam in the family Hiatellidae.

The geoduck is native to the coastal waters of the eastern North Pacific Ocean from Alaska to Baja California.

[5] The precise longevity of geoducks can be determined from annual rings deposited in the shell which can be assigned to calendar years of formation through crossdating.

[2] Native to the west coast of Canada and the northwest coast of the United States (primarily Washington and British Columbia), these marine bivalve mollusks are the largest burrowing clams in the world, weighing in at an average of 0.7 kilograms (1+1⁄2 lb) at maturity, but specimens weighing over 7 kilograms (15 lb) and as much as 2 metres (6 ft 7 in) in length are not unheard of.

[17] Biomass densities in Southeast Alaska are estimated by divers, then inflated by twenty percent to account for geoducks not visible at the time of survey.

[19][20] The geoduck's high market value has created an $80-million industry, with harvesting occurring in the US states of Alaska, Washington, and Oregon and the Canadian province of British Columbia.

The Washington State Department of Health tests water and flesh to assure clams are not filtering and holding pollutants, an ongoing problem.

[22] Because geoduck have a much higher market value live, an additional $4.4 to $6.6 per kilogram or $2 to $3 per pound, this development has helped to stimulate the burgeoning industry.

[23] Geoduck farming grow-out and harvest practices are controversial,[24] and have created conflicts with shoreline property owners,[25][26][27][28] and concerns from nongovernmental organizations.

[29] However, the Environmental Defense Fund has found that bivalves (oysters, mussels, and clams) are beneficial to the marine environment.

[35] A 2004 draft biological assessment, commissioned by three of the largest commercial shellfish companies in the Puget Sound region, identified no long-term effects of geoduck farming on threatened or endangered species.

On Japanese menus in cheaper sushi restaurants, geoduck is sometimes substituted for Tresus keenae, a species of horse clam, and labeled mirugai or mirukuigai.