The Natisone is a 60km river in Slovenia and Italy. It flows for some time as a border river between Slovenia and Italy, continues in Slovenia and then crosses the border and continues in Eastern Friuli, in northeastern Italy. It is the main tributary of the Torre and a sub-affluent of the Isonzo. It has the pluvio-nival regime and belongs to the Adriatic Sea Basin.The Natisone is formed at 415m above sea level on the border between Friuli and Slovenia by the confluence of two streams: the Rio Bianco and the Rio Nero which spring from the Punta di Montemaggiore and Gabrovec mountains. Before the confluence with the Torre, it passes through the communes of Pulfero and Cividale del Friuli.