Tay (tā) [key], longest river of Scotland, 118 mi (190 km) long. It rises on Ben Lui in the Grampians as the Fillan and flows NE into Loch Dochart, where it is called the Dochart until it enters Loch Tay, 141/2 mi (23 km) long and 1 mi (1.6 km) wide. Turning SE at the junction with the Tummel River, its chief tributary, the Tay enters the North Sea through the Firth of Tay (25 mi/40 km long). The river has important salmon fisheries. Tay Bridge crosses the firth at Dundee. The original bridge collapsed (Dec. 28, 1879) during a storm, with the loss of 90 lives, and was rebuilt (1883–88).