Higher concentrations of butyltin compounds were found in mussels collected from Mers El Kebir shipyard, Arzew, a petroleum harbour (industrial), and Beni Saf fishing harbour. This suggested that maritime activities nearby the harbours play a major role as the source of BTs. Indeed, harbour of Arzew is frequented by voluminous tanker. TBT was the predominant compound in mussels collected from almost all the sampling locations; indicate the fresh input of TBT in harbours.