Dragonja is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Slovenia

Slovenia

Slovenia , officially the Republic of Slovenia , is a country in Central and Southeastern Europe touching the Alps and bordering the Mediterranean. Slovenia borders Italy to the west, Croatia to the south and east, Hungary to the northeast, and Austria to the north, and also has a small portion of...

, in the northern part of the Istrian peninsula

Istria

Istria , formerly Histria , is the largest peninsula in the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Bay of Kvarner...

. It is the third longest river in Istria, after Raša

Raša (river)

The river Raša, in Croatian Istria is a major river of Croatia's Istria County. Its mouth is in the long ria of Raški zaljev/Porto d'Arsia, which is a drowned river valley scoured out when world sea levels were lowered, then drowned by the rising waters of the post glacial era...

 and Mirna

Mirna River (Croatia)

The Mirna is a river in Istria, Croatia. It is Istria's longest and richest river, being long and having a basin covering an area of . It rises near Buzet, and empties into the Adriatic Sea near Novigrad.-External links:* *...

.

The river is 28 kilometres (17.4 mi) in length and flows into the Gulf of Piran

Gulf of Piran

The Gulf of Piran or Piran Bay is located in the northern part of the Adriatic Sea, and is a part of the Gulf of Trieste. It was named after the town of Piran, and its shores are shared by Croatia and Slovenia. It is delimited by a line connecting Cape Savudrija in the south to the Cape Madona ...

.

In the lower reaches of Dragonja, there is a territorial dispute between Slovenia and Croatia

Croatia

Croatia , officially the Republic of Croatia , is a unitary democratic parliamentary republic in Europe at the crossroads of the Mitteleuropa, the Balkans, and the Mediterranean. Its capital and largest city is Zagreb. The country is divided into 20 counties and the city of Zagreb. Croatia covers ...

: while Croatian authorities claim that Dragonja is a border river, Slovenia claims a strip of territory south to the river, as well.