The Soča River, the main waterway of this area (about 136 km. long), finds its origin in Slovenia (the source is the Trenta Valley), flows through about 100 km., then rapidly towards the Italian territory, near Gorizia in Friuli Venezia Giulia and finally towards south into the Adriatic Sea. Its basin extends over the slovenian and italian territory with a total area of about 3416 km.2. Its name derives from the latin word "Aesontium" or "Sontium".
The main affluents are the slovenian Coritenza and Idria and the italian Torre (with the affluents Natisone and Judrio) and Vipacco. Slovenian towns and cities along its course include Bovec, Kobarid, Tolmin, Most Na Soči and Nova Gorica while in Italy, once left the mountain near Gorizia, it opens into a vast plain that extends on the northern side to the Collio Sloveno and south to the Lagoon of Grado. Around its mouth wild lands, green oasis and unspoiled spaces, such as Cona and Val Cavarera can still be found.
A wonderful waterfall of 15 meters and its varied course between two countries make the Soča River view spectacular and breathtaking; over the centuries, the river and its affluents have incised many stretches and created deep narrow rocky gorges that can still be admired by the most careful tourists. But perhaps even more spectacular is the bright green color of its waters, which earned it the name of "emerald beauty"; it is considered to be one of the rarest rivers in the world that retain such a colour throughout their course. It is no accident that the inhabitants consider the river the undisputed symbol of natural perfection.
Giuseppe Ungaretti, one of the greatest italian poets, mentions the river in his poem "The Rivers"; the slovenian poet Simon Gregorcic felt so inspired by this natural beauty that wrote his best-known poem "Soči" (meaning "To the Soča") one of the masterpieces of slovene poetry; this place offered its location for the famous Disney series "Chronicles of Narnia" in 2008; the Soča River is also well known for the endangered species "Salmo Marmoratus" (known as the marble trout).
The river also has an important historical value, here, in fact, took place the Battle of the Frigid River in 394 between the Eastern Emperor Theodosius the First, at the head of the Christian army, and the western Roman ruler Flavius Eugenius, at the head of the heathen soldiers, furthermore it was also a strategic place for the most important military operations on the Italian front from 1915 to 1917 during the First World War, where more than 300000 Italian and Austro-Hungarian soldiers lost their lives.