It rises at an elevation of 1,200 metres (3,900 ft) in the Ligurian Apennines on the north-west slopes of Monte Lama (near Monte Menegosa), within the commune of Morfasso. After about 15 kilometres (9 mi), at an elevation of 341 metres (1,119 ft), it is dammed to form the Lago di Mignano reservoir which covers about 2 square kilometres (0.77 sq mi) and provides both a water supply and hydro-electric power.
The Arda follows the typical pattern of an Apennine torrent with maximum discharges during the spring and autumn rains and a minimal flow during the summer.