The Drina River follows the border between Serbia and Bosnia and Herzegovina, so you can freely swim from one country to the other. Still, this is not recommended since the Drina river is a very fast river. This is why it is very popular for regattas (kayaking and rafting).
The Drina river is formed by the confluence of the Tara and the Piva rivers which come from Montenegro and it flows into the river Sava near the village called Bosanska Rača in Serbia. Together with its source river Tara (which comes from Montenegro), the Drina river is 487 km long but neither one is navigable.
Perućac lake on the Drina river is a very popular fishing destination. Throughout the summer months, the riverside of the Drina river is full of tourists, mainly from the Balkans’ countries.