The Una (, ) is a border river between Bosnia and Herzegovina and Croatia and a right tributary of the Sava river. It is part of the Black Sea drainage basin, and its watershed has a size of , of which belongs to Bosnia and Herzegovina, and to Croatia. The total length of the river is . The source of the river is located in the town of Donja Suvaja in Croatia, and its mouth is located near the town of Jasenovac, on the border with Bosnia. The largest right tributaries are the Krka, Unac, Krušnica and Sana rivers, and the largest left tributary is the Klokot river. Its longest headwater is the Unac river. The largest and most important city located on the river is Bihać. Other, important cities and towns are Bosanska Krupa, Bosanski Novi and Bosanska Kostajnica. The river is characterized by a multitude of waterfalls, rapids, karst springs and relatively untouched nature. A large part of the upper river is part of the Una National Park. Etymology According to local legends, the river was named by the Romans who, after seeing it for the first time, said una (lat. one, as a reference to its unique beauty) to describe it. Una is a popular female name even in the areas that are not located in the vicinity of the river. One explanation for this is that people that were displaced during the Yugoslav Wars continued to give the name to their children. Geography Sources The source of the Una river is located near the Croatian town of Donja Suvaja and consists of multiple smaller springs. The largest spring by discharge is a large karst spring at an elevation of above sea level, called Vrelo Une, and is considered to be the main spring of the river. The water, originating from great depths, forms a round, calm, bluish green lake, thirty meters by fifteen meters in size, surrounded by forests and steep cliffs of the Lička Plješevica and Stražbenica mountain ranges. The Una river, flowing out of the spring, forms its first travertine cascade roughly 20 meters downstream and another large waterfall 3 – 4 meters in height roughly 100 meters downstream. The spring itself was explored and mapped up to a depth of 248 meters, which makes it the deepest explored spring in the Dinaric karst region and the fifth deepest in the world. Due to