This oyster occurs from Baja California to Sitka Alaska. It is found mainly in the lower intertidal and shallow subtidal zones of sheltered saltwater lagoons and estuaries. Historically, Olympia oyster stocks were very large in the inland waters of Washington and British Columbia. Washington stocks now are limited to scattered areas throughout Puget Sound and Hood Canal. Population size and trend estimates are not available for the Olympia oyster in British Columbia, however anecdotal evidence indicates that the speciesÕ population levels are low in Georgia Strait relative to historic levels. There is evidence that pollution has been the primary factor in the demise of the Olympia oyster throughout lower Puget Sound and Hood Canal. Overharvesting has been identified as the leading cause of Olympia oyster stock crashes in Samish Bay. Factors that may be preventing the recovery of this species include introduction of non-native species such as the Japanese oyster drill (Cerateotoma inornatum), flatworms (Pseudostylochus ostreaophagus), and the copepod Mytilicola orientalis. Predation by native predators such as sea stars and diving ducks and competition with the introduced Pacific oyster (Crassostrea gigas) for space and setting habitat also may be hindering recovery of Olympia oysters. Factors involved in the decline of this species in Canada have not been studied. The Canadian Committee for the Status of Endangered Wildlife lists them as species of special concern. They are candidates for listing by Washington State. For more information about this species, visit the Pacific Biodiversity Institute website.