Volkhovsky District
The source of the Syas is in the Valday Hills north of the settlement of Nebolchi. The river flows north and enters Leningrad Oblast. It crosses the Tikhvin Ridge from the south to the north. Further north, it accepts the Tikhvinka from the right and turns west. There it accepts the Lunenka from the left, turns northwest and crosses into Volkhovsky District. The mouth of the Syas is downstream from the city of Syasstroy.