The distribution and accumulation of butyltins in various tissues of 13 benthic and pelagic species living in the sub-Arctic Saguenay Fjord (Canada) were investigated. Butyltin contamination was ubiquitous in this ecosystem with tributyltin (TBT) biota to sediment accumulation factors (BSAF) ranging between 0.22 and 11, but without any important biomagnification between trophic levels. The large range of butyltin compounds accumulating within different tissues of the species collected from all trophic levels was from 7 to 1238 ng Sn g(-1) d.w. and indicates an exceptional contamination level only found in northern coastal areas exposed to an intensive traffic of commercial ships. Results show that bioaccumulation in organisms depends on three main factors: (1) the actual contamination level in their habitat, (2) their assimilation pathway by water, sediment or diet, and (3) their ability to metabolize TBT and excrete metabolites. By their lack of an efficient TBT degradation system, bivalves are subject to accumulate more butyltins (from 890 to 993 ng Sn g(-1) d.w. for TBT and from n.d to 138 ng Sn g(-1) d.w. for metabolites) whereas most burrow-dwelling organisms are able to degrade TBT and their butyltin levels ranged from 86 to 239 ng Sn g(-1) d.w. for TBT and from 7 to 106 ng Sn g(-1) d.w. for metabolites. Acadian redfish (Sebastes fasciatus) feeding preferentially on shrimps and small crustaceans rich in TBT showed a contamination level about three times higher than eelpout (Licodes vahlii). The latter species living in contact with the sediment and feeding on worms and other burrowing species had a lower proportion of TBT in their tissues. Finally, deleterious effects of butyltins in the Saguenay Fjord were assessed by the significant occurrence of Imposex in common whelk (Bucinum undatum) in two sites from Baie des Ha! Ha!. Results revealed that the effects of Imposex were accentuated close to the source of contamination, at Port-Alfred harbour, since the total of imposexed whelks collected at site A (the mouth of Baie des Ha! Ha!) was 12.5% and reached 52.6% at site B (Port Alfred). Although the incidence or frequency of imposex was low in site A compared to site B, the relative penile length index (RPL) values, a measure of the degree or severity of imposex, was similar at both sites indicating the presence of TBT with higher concentrations in site B.