The Olympia oyster lives along the west coast of North America, between southern Alaska and down to Panama. It typically makes its home in protected saltwater coves, lagoons and estuaries (saltwater rivers) where it is not disturbed by rising and falling tides. It is usually attached to submerged rocks and hard ground in shallow waters. In British Columbia, the Olympia oyster is found along the Georgia Strait, the west coast of Vancouver Island, and around Queen Charlotte Strait and Sound.

Smaller than most oysters, the Olympia oyster will be at most nine centimetres in length and more likely just six centimetres. It is oval, and like all oysters, has two shells connected by a hinge. Its larger lower shell is rounded like a cup, while the slightly smaller upper shell is flat - with its edges tucking inside the rounded shell. Its outer shell ranges in colour from white to dark purple while its inside shell can be white, iridescent green and purple.