夏西河是俄罗斯的河流，位于诺夫哥罗德州和列宁格勒州，从发源地瓦尔代高地往北流往拉多加湖，河口附近有小镇夏西斯特罗伊，从11月至4月结冰。

The Syas River (Russian:Сясь) 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 260 kilometres (160 mi) long, and the area of its basin 7,330 square kilometres (2,830 sq mi). The largest tributary of the Syas is the Tikhvinka River (right).