The Eurasian beaver experienced a severe reduction in its distribution during the past centuries as a consequence of intensive hunting by humans. However, as a result of human-assisted re-introduction projects and translocations along the European territory, the species has increased its range significantly. Since beaver was introduced in Spain, its distribution had been restricted to the Ebro Basin and its surroundings. In this note, we report the presence of the species outside its known range, in the western part of the Iberian Peninsula, near the border with Portugal. We estimated an expansion rate of 15 km per year along the Ebro basin and discuss why the presence of beaver in the western area seems a result of an unauthorised translocation. Finally, we examine some important aspects that need further discussion when dealing with translocation or reinforcement events.