Yes, you can scuba dive in Karlovac. The diving club “RK Žabac” organizes diving in these parts, and though they say Mrežnica river might be the best for scuba diving, Kupa is nice, and Kamanje itself is an amazing location to visit and just chill in nature. If you do decide to submerge, slow currents and a couple of meters depth make this location a nice first-time river dive.