Istria is the largest peninsula within the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Kvarner Gulf. It is shared by three countries: Croatia, Slovenia, and Italy, with 87% of surface area being part of Croatia. Croatia encapsulates most of the Istrian peninsula within Istria County.

The Dragonja is a 30-kilometre (19 mi) long river in the northern part of the Istrian peninsula. It is a meandering river with a very branched basin and a small quantity of water. It has a pluvial regime and often dries up in summer. It features very diverse living environments and is home to a number of animal and plant species. The Dragonja has been a matter of a territorial dispute between Croatia and Slovenia, with its lowest portion de facto the border of the two countries.