The Una River carves a 212-kilometre corridor through the Dinaric karst, forming a natural boundary between Bosnia and Herzegovina and Croatia along its lower reaches. Designated a national park in 1953, the Una basin protects one of Europe's last free-flowing karst rivers, its turquoise waters fed by travertine springs and underground aquifers that maintain a constant 8–12°C year-round. The Štrbački Buk section, a tiered cascade dropping 24 metres over porous limestone barriers, anchors the park's core rafting corridor and marks the geographic threshold where the river curves toward the Croatian border. Una river rafting croatia tours navigate the twelve-kilometre stretch from Štrbački Buk to Lohovo, a Class II–III run threading travertine pools, submerged caves, and canyon walls that rise 80 metres above the waterline. The river's karst geology creates dynamic hydraulics: calcium carbonate precipitates into living barriers that shift seasonally, and spring melt from the Plješevica massif can raise water levels by two metres overnight. Rafters pass Martin Brod, a hamlet where the Unac tributary joins through a series of waterfalls, and enter the canyon's narrowest pinch — a 15-metre-wide chute flanked by forest canopy. The navigation fee, set at 12 BAM per person, funds trail maintenance and riparian monitoring within the park's 198-square-kilometre protected zone. The Una's position as a transborder waterway has shaped access protocols since the 1995 Dayton Agreement formalized the boundary. Croatian nationals and visitors holding Croatian entry permits can launch from Bihać, the Ottoman-era garrison town that serves as the park's administrative seat, and complete the run without crossing international checkpoints; the river corridor itself remains within Bosnia and Herzegovina, but the right bank opens to Croatian trailheads at three intervals. Outfitters operate under Bosnian licensing but coordinate with Croatian border authorities for multi-day itineraries that include the Zrmanja and Mrežnica rivers, both accessible within a two-hour transfer. The park's infrastructure expanded in 2018 with the construction of a visitor centre at Martin Brod, solar-powered raft storage at the Lohovo takeout, and a gravel access road that reduced shuttle times by 40 minutes. Seasonal flow data, published weekly during the April–October season, informs difficulty ratings: June runoff pushes the Štrbački section to Class III+, while late-summer baseflow drops it to Class II. The Una remains one of the few European rivers where commercial rafting coexists with endemic trout populations — brown trout and grayling spawn in the gravel bars that rafts glide over, a reminder that the corridor's value extends beyond recreation.