The Nestos river is the natural western border of Thrace. Its springs from Rila mountains in Bulgaria, crosses the mountains between Orvilos and Rodopi, and flows along the Thracian Tempi from Stavroupoli to Toxotes into the Thracian Sea. It is 234 km long. From Toxotes to its estuary, at a length of 27 km, the Nestos meets Kotza Orman, one of the most significant riparian water forests in Europe. The Nestos Delta is a wetland of international importance.

The river was worshiped as a sacred river by the Thracians and mentioned by ancient writers such as Herodotus, Thucydides, and Ptolemy. 

Nestos river and its delta