Although the rivers below are the longest in the United Kingdom, they are not close to being the longest rivers in the world (the Nile has a length of over 4000 miles). Nor are they among the longest rivers in Europe (the Volga is more than 2000 miles long).
The length of a river is measured by calculating the distance between the river’s source and its mouth.
The Top 20 Longest Rivers in the UK
(1) River Severn – 354 km (220 miles)
Not only is the River Severn UK’s longest river, but it is also the biggest in terms of its flow volume. Its source is in Plynlimon, Wales and it flows into the Severn Estuary (Bristol Channel). Its course takes it through the counties of Powys, Shropshire, Worcestershire, and Gloucestershire.
Learn more about the River Severn.
(2) River Thames – 346 km (215 miles)
The River Thames is England’s longest river, and it flows into the Thames Estuary (North Sea). Its course takes it through the counties of Gloucestershire, Wiltshire, Oxfordshire, Berkshire, Buckinghamshire, Surrey, Greater London, Kent, and Essex.
Learn more about the River Thames.
(3) River Trent – 297 km (185 miles)
The River Trent flows through the counties of Staffordshire, Derbyshire, Leicestershire, Nottinghamshire, Lincolnshire, and Yorkshire. Its mouth is the Humber Estuary. It often floods following heavy storms.
Learn more about the River Trent.
(4) River Wye – 250 km (155 miles)
For much of its course, the River Wye forms the boundary between England and Wales. Its source is in Plynlimon, Wales, and it flows into the Severn Estuary.
Learn more about the River Wye.
(5) River Great Ouse – 230 km (143 miles)
There are several rivers in the UK named the Ouse, but the River Great Ouse is the longest of them. It flows through the counties of Buckinghamshire, Bedfordshire, Cambridgeshire, and Norfolk, and it empties out into The Wash.
Learn more about the River Great Ouse.
(6) River Ure / River Ouse – 208 km (129 miles)
Located in North Yorkshire, the River Ure flows for 119 km through Wensleydale before it is named the River Ouse. The River Ure / River Ouse is the longest river to flow in just one county (Yorkshire), and it empties out into the Humber Estuary.
(7) River Tay – 188 km (117 miles)
The River Tay is the longest river in Scotland. Its source is Allt Coire Laoigh and it flows into the Firth of Tay (North Sea). Its drainage basin is about 5200 square km, making it the largest one of all of the UK’s rivers.
Learn more about the River Tay.
(8) River Clyde – 176 km (109 miles)
The River Clyde flows through the Scottish city of Glasgow. Its source is in the Lowther Hills in South Lanarkshire, and it empties into the Firth of Clyde.
Learn more about the River Clyde.
(9) River Spey – 172 km (107 miles)
The River Spey is Scotland’s fastest flowing river. Its source is Loch Spey, and it flows into the Moray Firth.
Learn more about the River Spey.
(10) River Nene – 161 km (100 miles)
The River Nene flows through the counties of Northamptonshire, Cambridgeshire, Lincolnshire. and Norfolk. Part of its course marks some of the border between Cambridge and Norfolk. It empties out into The Wash.
Learn more about the River Nene.
(11) River Bann / Lough Neagh – 159 km (99 miles)
The combined length of Northern Ireland’s Upper Bann, Lower Bann, and Lough Neagh is 159 km. Its source is in Slieve Muck, County Down, and it empties into the Atlantic Ocean at Portstewart.
Learn more about the River Bann.
(12) River Tweed – 155 km (96 miles)
The River Tweed is sometimes referred to as Tweed Water. It is located in Scotland and flows into the North Sea at Berwick-upon-Tweed. It is one of the best salmon rivers in the UK.
(13) River Avon – 154 km (96 miles)
The River Avon is one of the River Severn’s main tributaries. It flows through the counties of Northamptonshire, Leicestershire, Warwickshire, Worcestershire, and Gloucestershire. It joins the River Severn at Tewkesbury.
Learn more about the River Avon.
(14) River Eden – 145 km (90 miles)
Located in Cumbria, the River Eden’s source is at Black Fell Moss, Mallerstang, and it flows into the Solway Firth. It is crossed by Hadrian’s Wall.
Learn more about the River Eden.
(15) River Dee – 140 km (87 miles)
Located in Aberdeenshire in Scotland, the River Dee flows into the North Sea at Aberdeen. Its course takes it through Royal Deeside, the location of the Royal residence, Balmoral Castle.
Learn more about the River Dee.
(16) River Witham – 132 km (82 miles)
The majority of River Witham’s course is in the county of Lincolnshire. It flows through the town of Grantham, and the city of Lincoln, and empties out into the Haven (in Boston, Lincolnshire).
Learn more about the River Witham.
(17) River Teme – 130 km (81 miles)
The River Teme’s source is in Dolfor (Wales), and it flows through the counties of Powys, Shropshire, Herefordshire, and Worcestershire. It empties out into the River Severn at Powick in Worcestershire.
Learn more about the River Teme.
(18) River Don – 129 km (80 miles)
Located in north-east Scotland, the River Don flows through Aberdeenshire into the North Sea. Its source is in the Grampian Mountains.
(19) River Foyle – 129 km (80 miles)
The River Foyle is formed when the River Finn and the River Mourne combine, and it flows into Lough Foyle. Its course takes it through the counties of Donegal, Tyrone, and Londonderry.
Learn more about the River Foyle.
(20) River Usk – 125 km (78 miles)
Located in Wales, with a source in Fan Brycheiniog, Powys, the River Usk flows through the counties of Powys, Carmarthenshire, Monmouthshire, and Newport. It empties into the Bristol Channel.
Learn more about the River Usk.
Discover more river facts and learn more about other record-breaking rivers by visiting our rivers resources page.