Albert Barnes Commentary Ezra 8:15

"And I gathered them together to the river that runneth to Ahava; and there we encamped three days: and I viewed the people, and the priests, and found there none of the sons of Levi." — Ezra 8:15 (ASV)

Ahava was both a town and a river (Ezra 8:21). The modern name of the place is Hit. It is famous for its bitumen springs, and is situated on the Euphrates, at a distance of about 80 miles from Babylon, toward the northwest.

None of the sons of Levi - The Levites appear to have been disinclined to return to Jerusalem (see Ezra 3:8 note).