The Sviyaga (Russian: Свияга, Tatar Cyrillic: Зөя, Latin: Zöyä, Chuvash: Сĕве) is a river in the Ulyanovsk Oblast and Tatarstan, a right tributary of the Volga River. It is 375 kilometres (233 mi) long, and its drainage basin covers 16,700 square kilometres (6,400 sq mi). The Sviyaga River flows into the Sviyaga Cove of the Kuybyshev Reservoir, west of Kazan. It freezes up in November or December and stays under the ice until April or May. Major tributaries are the Arya, Bula, Karla, Kubnya, and Tosha rivers.
The city of Ulyanovsk is along the Sviyaga River. In Ulyanovsk, the Sviyaga flows only a few miles away from the Volga, but their confluence is about 200 kilometres (120 mi) north of Ulyanovsk.
The castle of Sviyazhsk, which dates to 1551, is on the island in Sviyaga Cove of the Kuybyshev Reservoir.
Coordinates: 55°43′52″N 48°36′57″E / 55.73111°N 48.61583°E