The Daysan River (also spelt Daisan and known in Arabic as Al-Jullab or as Daysan) was the name of a perennial river that flowed through the city of Urfa (historically called Edessa and known in Arabic and Syriac as al-Ruha') in the Arabian Plate.
A combination of 25 streams, it ran through Urfa and Harran (ancient Carrhae) before joining the Balikh river (also spelt Belichas), one of the largest tributaries to the Euphrates, at ancient Dabanas (modern Dibni) in Raqqa in the Eastern Mediterranean conifer-sclerophyllous-broadleaf forests ecoregion. Today it runs dry before reaching the Balikh, and numerous dried-up wells in the old city of Harran suggest that the water table may have been significantly higher in the past.