Similar to the zebra mussel (Dreissena polymorpha) and the quagga mussel (Dreissena bugensis), the Asian clam (Corbicula fluminea) is an invasive bivalve that has colonized many waterbodies in the United States and Europe. So far, low water temperature and ice formation during winter appear to have limited its northern distribution, especially in Eastern North America. This paper documents the recent discovery of a Corbicula fluminea population in the St. Lawrence River, in the thermal plume produced by the Gentilly-2 nuclear power plant (Becancour, Quebec, Canada). Based on a benthic samples obtained during November 2009 from 21 sites, both upstream and downstream of the power plant outlet, average density (+/- standard error) of this non-indigenous species was 368 +/- 176 living individuals/m(2). Additional samples collected in 2010 showed an increase in density to 3,380 +/- 1,315 living individuals/m(2) downstream the power station, and established the range limit at 4 km downstream. The species was present only downstream of the power plant and its distribution appears to be associated with the warm water plume. The influence of the thermal plume at 4 km from the power station was however fairly limited. The size of individuals varied from < 1 mm to 24 mm in length. These results confirm the establishment of the species in the St. Lawrence River, thereby extending the northern boundary of its distribution in North America.