Nidelva (also known as Nidelven) is a river in the county Sør-Trøndelag, Norway. "Elv" in Norwegian means river, so a more accurate translation may be "the river Nid". It starts at the west-end of Selbusjøen (the largest lake in Sør-Trøndelag) at Brøttem and runs via Tiller and at the end through the city of Trondheim before reaching the Trondheimsfjord. There are six hydro-electric power stations along the river. The tributary river that empties into Selbusjøen is called Nea.