Rainbow smelt Osmerus morda\. introduced into the Great Lakes watershed (Crystal Lake, Michigan) in about 1912, began coloni/ing the Great Lakes in the 1920s. The species now is found throughout much of the Great Lakes watershed of Ontario and in the Mississippi-Missouri drainage as a result of inadvertent or intentional introductions. Gill-net and trawling surveys in 1989 and 1990 of 79 lakes (92 separate times or sites) in the Winnipeg River svstem of the Hudson Bay drainage in northwestern Ontario, southeastern Manitoba, and northeastern Minnesota revealed or confirmed the presence of rainbow smelt in 19 lakes and extended the species* known range in the Rainy, English, and Wabigoon river systems. Rainbow smelt also were discovered in Lake Winnipeg late in 1990 and in Lake of the Woods in early 1991. Elsewhere, the establishment of rainbow smelt in new water bodies often has been associated with changes in native fish populations. The potential now exists for further spread of rainbow smelt in this watershed as far as Hudson Bay.