The Raša in Croatian Istria is a major river of Croatia's Istria County. It is 23 kilometres (14 mi) long, and its basin covers an area of 279 km2 (108 sq mi). Its mouth is in the long ria of Raša Bay, which is a drowned river valley scoured out when world sea levels fell, then drowned by the rising waters of the post-glacial era. The Raša rises in springs near Pićan and flows south through a steep-sided valley before opening into the head of the Adriatic Sea. The river, although short in length, has an ancient history as a border.

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.