The Syas River is a river in Lyubytinsky District of Novgorod Oblast and Tikhvinsky and Volkhovsky Districts of Leningrad Oblast, Russia. The Syas River flows from Valdai Hills north into Lake Ladoga. A town of Syasstroy is located at its mouth. It is long, and the area of its basin . The largest tributary of the Syas is the Tikhvinka River (right).