This species is endemic to northcentral Portugal, where it occurs in the basin of the rivers Mondego, Seia and Cobral (Sampaio 1946, Franco and Afonso 1994). Its geographic range is 1,043 km² (Commission of the European Communities 2009). It is very abundant along the Seia river valley and also abundant along the Mondego, but becomes more scarce along the river Cobral. It also occurs outside this area spread over the Mondego valley, until at least 30 km to the north. The area occupied by the species reaches at least 7,000 hectares. The sites outside the Mondego river were not surveyed, so that the occupied area might be bigger than expected (ICN 2006).