The source of the river is in the eastern Rhodope Mountains in the western Evros regional unit, Greece, near the village Mikro Dereio.

The Erythropotamos River basin covers an area of approximately 1,618.5 km², with most of it in Greece's Thrace region and a smaller part in Bulgaria.

The region's geological formations include orthogneisses, augen gneisses, pegmatites, marbles, amphibolites, and sediments.

Flood susceptibility mapping has been carried out using GIS and remote sensing technologies, identifying high-risk zones and validating them with SAR imagery.

[2] The Erythropotamos River has been affected by the introduction of invasive species, such as the Asian clam (Corbicula fluminea).