Tay, a river and loch of Perthshire, Scotland. The river rises in a small loch on the border of Argyleshire, and is called the Fillan until it passes through Loch Dochart, 8 or 9 m., and thence to Loch Tay, 10 m. further, it is generally known as the Dochart. Near Loch Tay it receives the Lochie, and below that loch the river Lyon and numerous other tributaries. It is nearly 120 m. long, and describes almost a semicircle, flowing mainly N. E. and S. E., until it reaches Perth, whence it flows nearly E. through the frith of Tay into the North sea. It has tide water and is navigable for vessels of 9 ft. draught to Perth. Above this point it flows through the finest valley of Scotland, and it discharges a larger volume of water than any other river of the British islands. Its salmon fisheries are celebrated. Loch Tay is about 16 m. long and 1 m. wide, with steep, precipitous banks, and is said to have been sounded to a depth of 600 ft. Ben Lawers, on its N. W. shore, rises to a height of 3,984 ft.