Smith's Bible Dictionary

Ulai (pure water) is mentioned by Daniel, (Daniel 8:2; Daniel 8:16) as a river near to Susa, where he saw his vision of the ram and the he-goat. It has been generally identified with the Eulaeus of the Greek and Roman geographers, a large stream in the immediate neighborhood of that city. The Eulseus has been by many identified with the Choaspes, which is undoubtedly the modern Kerkhah, an affluent of the Tigris, flowing into it a little below Kurnah. Recent surveys show that the Choarspes once divided into two streams about 20 miles above Susa. The eastern was the Ulai. This bifurcation explains (Daniel 8:16)