The range of Gasterosteus aculeatus encompasses the coastal waters of Eurasia, Iceland, eastern Asia and Northern America. In North America, this fish ranges from Alaska to Baja California on the west coast, from Baffin Island and the west side of Hudson Bay to Chesapeake Bay, Virginia, along east coast, and it occurs also in inland areas (including Lake Ontario) along both coasts. Sometimes this species occurs in the open ocean. This species has been introduced and is established in certain areas of California, Massachusetts, and the Great Lakes (Lakes Huron, Michigan, Erie and Superior) (Fuller et al. 1999; Stephenson and Momot 2000). In Eurasia it is found along North Sea coasts of Scotland and Scandinavia; coasts of Iceland and White Sea; Atlantic coasts from Ireland northward; southeastern shore of Baltic Sea and its basin (Odra and Vistula drainages); shores of Black Sea and its northern basin (from Danube to Kuban drainages). Almost absent inland in Finland, except north of 68°N. There is a hybrid zone with G. gymnurus in the English Channel, southern North Sea, Baltic Sea and their basins. It has been introduced to northern Italy.