In the Song of Deborah, which river swept Sisera's forces away?

Answer: The Kishon

Deborah sang that the stars fought against Sisera and "the River Kishon swept them away, the ancient river" (Judges 5:20-21).

“From the heavens the stars fought; from their courses they fought against Sisera. The River Kishon swept them away, the ancient river, the River Kishon. March on, O my soul, in strength!”— Judges 5:20-21 (BSB)