River Tay River Tay The River Tay () is the longest river in Scotland and the seventh-longest in the United Kingdom. The Tay originates in western Scotland on the slopes of Ben Lui (), then flows easterly across the Highlands, through Loch Dochart, Loch Iubhair and Loch Tay, then continues east through Strathtay (see Strath), in the centre of Scotland, then southeasterly through Perth, where it becomes tidal, to its mouth at the Firth of Tay, south of Dundee. It is the largest river in the UK by measured discharge. Its catchment is approximately , the Tweed's is and the Spey's is
Inner Tay Estuary reedbeds. There are two large islands: Mugdrum Island opposite Newburgh and Moncreiffe Island immediately below Perth. The narrow form of the estuary and the large volume of freshwater from the Rivers Tay and Earn restrict the influence of salt water west of the Tayport narrows. Much of the tidal water in the estuary is freshwater or mildly brackish. The 20 km or so stretch between the railway bridge and the confluence of the Rivers Tay and Earn is a site of special scientific interest. The current SSSI was notified in August 1999 and extends to 4,115 hectares or thereby. Scottish