The Enns (, ) is a southern tributary of the river Danube, joining northward at Enns, Austria. It forms much of the border between the states of Lower Austria and Upper Austria. The Enns spans , in a flat-J-shape. It flows from its source near the village Flachau, generally eastward through Radstadt, Schladming, and Liezen, then turns north near Hieflau, to flow past Weyer and Ternberg through Steyr, and further north to the Danube at Enns (see map in References). Name It was known in Latin as Anisus or Anasus, of uncertain origin; Anreiter et al. tried to link it to an Indo-European *on- and the hydronymic suffix *-is-. Later sources call it Ensa or Enisa. Others have linked it to Upper Danubian Vasconic *an, "water." Another possible link is Greek ᾰ̓νῠστός (anystos, "useful"). The West Slavic languages have different names for the river: in Czech it is called the Enže; in Slovak, the Enža; and in Polish, the Aniza. Geography The Enns has its source in the Radstädter Tauern mountains in the Austrian state of Salzburg. In a valley which developed during the ice age, it flows at the border between the Northern Limestone Alps and the Central Eastern Alps on an eastern trajectory through Styria, where it passes the Dachstein group at its southern side. Between Admont and Hieflau, it takes a turn to the North and passes through the Gesäuse, a gorge of a length of , where it penetrates the limestone of the Ennstaler Alpen. Flowing to the north from there on, it reaches the state of Upper Austria at the mouth of the . North of Steyr, it forms the border between Upper Austria and Lower Austria (formerly also known as Austria above the Enns and Austria below the Enns). Finally, it meets the Danube at Mauthausen and the city of Enns. It is the longest river solely in Austria. The Enns is a typical wild water river and draws its water from an area of , which makes it the fifth-largest in Austria. Its average discharge at the mouth is . The Anisian Age in the Triassic Period of geological time is named from Anisus, the Latin name of the river Enns. History In the middle of the 19th century, canals began to be built along the between Weißenbach and the Gesäuse, in order to make use of the water for agriculture and forestry.