Kosynthos, also known as Kompsatos or Kosinitis, is one of the most important rivers in Thrace that flows through the city of Xanthi. Its total length is 55 kilometers. It springs from Rhodope mountain range and flows in Vistonida lake. For most of its route, through the regional units of Xanthi and Rodopi, the river traverses a course in the mountains, between small valleys and deep ravines with wooded slopes and impressive formations of high and steep cliffs. Small waterfalls and lakes are formed in many parts of the riverbed.
Oak and pine forests spread all over the area and beech trees meet them along the Greek-Bulgarian borders. The area is the habitat of wild animals mainly, mammals as well as birds, some of which are in danger of extinction.
In the city of Xanthi, Kosynthos flows through the neighborhoods of the Old Town and Samakov, heading towards lowland areas up to its estuary in the northern part of Vistonida lake.