The river's name, which was recorded in 781 as Alera, in 803 as Elera, in 1096 as Alara, has two possible derivations: .
A shortened form of *Eleraha, where *Eler in Old German *olisa or Old Slavic olsa (Polish: olsza) would mean Erle ("alder") and aha (pronounced in German: Acha) is an old word frequently used in river names to mean "water" (c.f. the Latin aqua).