River Tay
The River Tay emerges from Loch Tay at Kenmore, and flows from there to Perth which, in historical times, was its lowest bridging point. Below Perth the river becomes tidal and enters the Firth of Tay. The largest city on the river, Dundee, lies on the north bank of the Firth. On reaching the North Sea, the River Tay has flowed from west to east across central Scotland.
Cheddar Yeo
The Cheddar Yeo is a small river in Somerset, England. Beneath the limestone of the Mendip Hills it forms the largest underground river system in Britain. After emerging into Cheddar Gorge it flows through the village of Cheddar, where it has been used in the past to power mills. From the Middle Ages until the 19th century the river had ports for seagoing vessels but is no longer navigable. Some of the water, which is of good quality, is diverted into Cheddar Reservoir to provide drinking water for Bristol.