Kupa (Slovenian Kolpa) is a river in Croatia and on the border with Slovenia.

The Kupa originates in the mountainous region of Gorski Kotar , northeast of Rijeka, flows a few kilometers eastwards before reaching the Slovenian border. It then continues eastwards, passes Vrbovsko, and eventually detaches from the Slovenian border. It then reaches the city of Karlovac, where it receives influx from two other rivers from the right, Dobra and Korana (which in turn is joined by Mrežnica ). It continues flowing to the east, where it merges with Glina from the right as well as Odra from the left, and proceeds to the city of Sisak where it flows into the Sava.