Boka is a karst spout , waterfall and torrential stream, which is a right tributary of the Soca . The length of the stream to the mouth of the Soca is less than one kilometer , making it one of the shortest rivers in Slovenia . Boka is the height of 106 m and a width of 18 m undoubtedly the most glorious waterfall in Slovenia . If we add the 33 m high waterfall below , we get a height of 139 meters which makes it probably the highest waterfall in Slovenia. In the driest periods it has a flow of two cubic meters per second , the abundant rainfall increases circulation to the majestic hundred cubic meters per second . Boka stream collects water in the Kanin mountain range , and then flows through the underground and comes out on the rocky ledge which runs at about 30 m . The waterfall is still growing , as are the rocks on which it falls are less resistant than the threshold over which it pours .