Aller River Nature · Aller, Caudal, Asturias It rises at the Vegarada pass and runs for some 38 kilometres through the municipality to which it gives its name before joining the Lena at Ujo to form the Caudal. According to García Arias its name comes from the Indo-European root *al-, "white", found in other river names in the region. Photo: Carmenmoran (CC BY 4.0) What to see and do in Aller