All measurements have been recalculated using data supplied by the Scottish Environmental Prptection Agency (SEPA) and ordnance survey maps as published in August 2010. Data obtained from this page prior to September 2010 is obsolete and should not be used
Rank Name Length Source Course of Waterway Notes Mouth  
    miles Km          
1 TAY-TUMMEL-GAUR 114.9 184.9 Coirean Lochan by Stob Ghabhar (NE face), 9km NW of Bridge of Orchy Firth of Tay-R.Tay-R.Tummel (incl L.Faskally & L.Tummel & Dunalastair Water)-L.Rannoch-R.Gaur- L.Eigheach-Garbh Ghaoir- L..Laidon- Abhainn Ba- L Ba - R.Ba see note 1 North Sea between Broughty Ferry and Tayport  
1b TAY-DOCHART 114.0 183.4 Beinn Oss (S. face), 10km W of Crianlarich Firth of Tay-R.Tay-L.Tay-R.Dochart-L.Iubhair-R.Fillan-R.Cononish-Allt Coire Laoigh      
1c TAY-LYON 107.1 172.4 between Beinn a' Chaisteil and Cam Chreag Firth of Tay-R.Tay-R.Lyon-L.Lyon-Abhainn Ghlas see no.28 and note 1    
2 SPEY 104.8 168.6 Coire Shesgnan, 12km NW of Kinloch Laggan Spey Bay-R.Spey (incl L.Insh & Spey Reservoir)-Shesgnan Burn see note 2 North Sea at the bar of Spey Bay  
3 CLYDE 104.6 168.4 Shiel Dod (S.face), 5Km W of Durisdeer R.Clyde-Daer Water(incl Daer Reservoir)-Thick Cleuch-Yaud Stell Burn see note 3 Firth Of Clyde at Ardmore Point  
4 TWEED 100.5 161.8 between Barncorse Knowe and Whitehope Knowe, 9.5km  N of Moffat R.Tweed- Cor Water- Powskein Burn   North Sea between Berwick-upon-Tweed pier and Sandstell Point, Spittal (England)  
1d TAY-TUMMEL-GARRY 97.5 157.0 Sgairneach Mhor(W face), 6k W. of Dalnaspidal  Firth of Tay-R.Tay-R.Tummel(incl L.Faskally-R.Garry-L.Garry- Allt Shallain-All tna Glaise      
5 DEE   (Aberdeenshire) 88.4 142.7 Braeriach(w side) R.Dee-Allt a'Gharbh choire   North Sea at Footdee, Aberdeen (excludes length of north pier)  
4b  TWEED-ETTRICK 85.0 136.8 Capel Fell (E face), 8km E of Moffat R.Tweed- Ettrick Water- Black Burn      
1e TAY-ISLA 84.7 136.3 Cairn of Claise (E.face), 5.5km E of Glenshee Ski centre Firth of Tay-R.Tay-R.Isla-Canness Burn see no.19 and note 1     
6 FORTH 84.3 135.7 S face of S top of Cruachan, 2.5km SW of Inversnaid R.Forth- Duchray Water-Abhainn Gaoithe see note 6 Firth of Forth at the easternmost point of Inch Garvie by the Forth Bridge.   
7 DON 83.8 134.9 Well of Don, 6.5km W of Cockbridge R.Don-Allt Tuileach- Feith Bhait-Ailtan Mhicheil   North Sea, near Bridge of Don, Aberdeen  
6b FORTH-TEITH 75.3 121.2 between Parlan Hill and Creag Bhreac Mhor, 4Km E of Ardlui R.Forth- R.Teith-Garbh Uisge/R.Leny- L.Lubnaig-R.Balvag- L. Voil.- R. Larig see note 6    
4c TWEED-TEVIOT 70.5 113.5 Between Stock Hill and Eweslees Knowe (E side of Stock Knowe) R.Tweed-R.Teviot-Ramsaycleuchburn see no.24    
2b SPEY-AVON 70.5 113.4 E face of Ben Macdui R.Spey- R.Avon-L.Avon-Garbh Uisge Mor see no.25    
8 NESS-OICH-GARRY 67.7 108.9 between Sgurr na Ciche and Gharbh Chioch Mhor, 16km N of Glenfinnan R.Ness-L.Ness-R.Oich-L.Oich-R.Garry (incl L.Garry and L.Poulary)-Gearr Garry-L.Quoich-Allt Coire nan Gall-Allt Bealach na h-Eangair   Beauly Firth at Inverness (by marina)  
9 FINDHORN 64.1 103.2 South Side of Carn Odhar na Criche, 9km N of Laggan Bridge R.Findhorn-Abhainn Cro Chlach   Moray Firth at Findhorn  
1f TAY-EARN 63.8 102.6 Loch Earn Firth of Tay-R.Tay-R.Earn see no.21 and note 1     
10 NITH 62.6 100.8 Between Prickeny Hill and Enoch Hill, 7km E of Dalmellington R.Nith see note 10 Solway Firth at Airds Point  
11 DEVERON 62.3 100.2 North side of Creag na Gamhna, 7.5km N of Strathdon R Deveron- Allt Deveron-Burn of Rochford-Burn of Hillocks   North Sea at Banff Bay  
12 BEAULY-GLASS-AFFRIC 58.0 93.4 South east side of Sgurr a'Bhealaich Dheirg, 11km SE of Shiel Bridge Beauly Firth-R. Beauly-R.Glass- R.Affric (incl. L. Beann a Mheadhoin & L.Affric)- Allt Cam Ban see note 12 Moray Firth at River Ness  
13 CONON 54.8 88.3 Cul Leathaid, N side of Carn Breac, 8km S of Kinlochewe Cromarty Firth-R.Conon(incl. L.Achonachie)-L.Luichart-R.Bran(incl.L.Achanalt)-Abhainn Loch a'Chroisg-L.a'Chroisg-Abhainn Dubh (incl. L.Crann & L.Phiarlaid) see note 13 Moray Firth by Nigg Bay at Invergordon Harbour/ Newhall Point  
14 DEE-KEN-WATER OF DEUCH   (Galloway) 54.7 88.0 North east face of Windy Standard, 14.5km ESE of Dalmellington. R.Dee-L.Ken-Water of Ken (incl. Earlston Loch)-Water of Deuch see note 14 Irish Sea at Kirkcudbright Bay  
15 LOCHY-SPEAN 54.0 86.9 south face of Sron Bealach Beithe (by Ben Alder), 15km NE of Rannoch Station R.Lochy-R.Spean (incl. Lower L.Laggan)-L.Laggan-R. Pattack-L.Pattack- Allt a Chaoil-reidhe - Allt a'Bhealaich Bheithe (incl. L.a'Bhealaich Bheithe)   Loch Linnhe at mouth of River Nevis  
16 SOUTH ESK 52.7 84.8 between Fafernie and Cairn Bannoch, 11km SE of Braemar R.Soth Esk (incl Montrose basin)-Burn of Fafernie   North Sea at Montrose  
3b CLYDE-LEVEN-ENDRICK 50.4 81.0 West side of Gargunnock Hills, above Standmilane Craig, 4km SE of Kippen R.Clyde-R.Leven-L.Leven-Endrick Water-Backside Burn-Gourlay's Burn      
13b CONON-MEIG 49.2 79.2 Lochan Gaineamhach, NW of Sgurr a'Charoachain Cromarty Firth-R.Conon(incl. L.Achonachie)-R.Meig (incl. L.Meig and L. Beannacharain)-Ann crom-alt - Allt an Lochan Gaineamhaich see note 13    
17 ANNAN 48.7 78.3 between Herman Law and Trowgrain Middle, 16km NE of Moffat R.Annan-Moffat Water-Birkie Cleuch   Solway Firth, south of Annan  
18 ESK 47.8 77.0 Bloodhope head, 6.5km Sw of Ettrick village R.Esk-R.White Esk-Tomleuchar Burn-Bloodhope Burn see note 18 Solway Firth, at River Sark  
19 ISLA 46.6 75.0 Cairn of Claise (E.face), 5.5km E of Glenshee Ski centre R.Isla-Canness Burn see note 1 River Tay, 2km  S of Meikleour  
20 OYKEL 45.6 73.4 Gharbh Choire, SE face of Conival (west top Ben More Assynt) Dornoch Firth-Kyle of Sutherland-R.Oykel (incl.L.Ailsh)-Allt an Dubh Loch'  Mhoir- Dubh Loch Mor - Allt a Gharbh Choire see note 20 North Sea at Cromarty Firth (A9) Bridge  
21 EARN 45.2 72.8 Loch Earn R.Earn see note 1 River Tay, 3.5km  W of Newburgh  
22 AYR 43.3 69.7 W face of Sclanor Hill, 5km NE of Muirkirk R.Ayr-Glenbuck Loch-Stottencleuch Burn   Firth Of Clyde at Ayr harbour  
23 NORTH ESK 41.5 66.8 NW side of Wester Balloch R.North Esk-Water of Mark-Tod Grain   North Sea, north of Montrose  
24 TEVIOT 41.3 66.5 Between Stock Hill and Eweslees Knowe (E side of Stock Knowe) R.Teviot-Ramsaycleuchburn   River Tweed at Kelso  
25 AVON   (Moray) 39.7 63.9 E face of Ben Macdui R.Avon-L.Avon-Garbh Uisge Mor   River Spey, 1.5km N.of Bridge of Avon  
26 YTHAN 39.1 63.0 East side of Ythanwells village R.Ythan   North Sea near Newburgh, Aberdeenshire  
27 LOSSIE 36.4 58.6 Clash Gour, North side of Carn Kitty R.Lossie (incl. L.Trevie)   North Sea at Lossiemouth  
28= NAIRN 35.7 57.5 W side of Carn Ghriogair R.Nairn- Cromm Allt Beag   Moray Firth at Nairn  
28= LYON 35.7 57.5 between Beinn a' Chaisteil and Cam Chreag R.Lyon-L.Lyon-Abhainn Ghlas   River Tay, 3km NE of Kenmore  
30 ERICHT-ARDLE 32.9 53.0 W face of Carn an t-Sionnaich, 11km NNW of Spital of Glenshee R.Ericht-R.Ardle-Allt Fearnach see note 1 River Isla, 3km NE of Coupar Angus  
Measurements have, where possible, been correlated with those supplied by the Scottish Environment Protection Agency (SEPA) who are responsible for the protection of Scotland's rivers. However SEPA's data sheets do not include measurements for what it regards as estuaries which in the case of the Forth means downstream of the railway bridge at Stirling, and for the Clyde means downstream of Glasgow city centre. Neither do they include lengths of major lochs through which a river flows. In addition, the length they give for the upper reaches of a river may add together the lengths of more than one headstream, thus potentially overstating the length of the river. Where Sepa does not supply usable data, the lengths have been measured directly from the appropriate Ordnance Survey maps 
For estuaries the principle followed is that the river should be visible at all times. The measurement therefore follows the centre of the river at low tide and the mouth of the river is assumed to be at the coastal high tide mark. This does not generally make a significant difference, except for rivers draining into shallow sloping sands of the  Irish Sea and Solway Firth, notably the Nith.
Where a river flows through a loch, the length of the loch is included. Thus the length of the Tay-Dochart includes Loch Tay. This is normal practice- the quoted length of the Nile includes Lake Nasser. Indeed many lochs can be regarded as simply broadenings of rivers and it can be difficult to tell where a loch begins, as illustrated by the fact that the Ordnance Survey labels one stretch of water as "Loch Ken or River Dee". The length of river included is the shortest distance of water between where the river flows into the loch and where it leaves it. 
The source is normally taken as that of the furthest headstream of the river or a significant tributary. The only cases where the furthest headstream is not taken as a source is where a river flows out of a loch which is supplied by a number of streams, none of which is significant enough to be considered the main inflow of the river. In such a case the source is taken to be that loch. 
Tributaries are included in the numbered list provided they are not included in the overall length of the main river into which they flow. The distance of the headstreams of certain tributaries to the sea are also shown, but are not numbered in the consecutive list because the lower stretch of the river would be counted twice. Thus the Isla, a tributary of the Tay is listed as no.19, and ithe distance from the source of the Isla to the sea is noted separately (1e) 
Note 1.-The Tay and its tributaries      
Previous authorities gave a distance of 119.4miles (192.2km) for the Tay-Tummel. This seems to be a combination of  taking the mouth at a line from Budden Ness to Tentsmuir Point which adds 4miles (6.4km) to the length, and using measurements taken before hydro-electric works replaced winding river with an extended loch.
The distances of the various stetches of the river Tay system are shown below. As distances are given to the nearest 100metres, adding the total measurements of stretches may be 100metres different from the total distance shown in the table above. 
  River Garry  52.1km   River Isla 75.0Km  
  Ba-Guar (35.9km) L Rannoch 16.1km Tummel(L. Rannoch- Garry) 28.1km River Tummel (Tay-Garry)13.3km      
  Lyon 57.5km     River Tay(Lyon-Tummel) 23.3km River Tay (Tummel-Isla) 30.3km   River Tay (Isla-Earn) 31.5km Firth of Tay
  River Tay (L.Tay-Lyon)4.4km   29.8km
    River Earn 72.8km  
  Fillan-Dochart  40.4km L Tay 23.7km  
Note 2.-The Spey
The source of the Spey is taken at its furthest headstream, as is the case with all the rivers listed. The course of the Spey itself, i.e. the whole of the river with the name Spey from its source, is 167.6km i.e. 1km less than the length from the source of the Shesgnan Burn. Using this length would make it shorter than the Clyde. However the Spey is the longest stretch of river in Scotland bearing the same name, though it does include Loch Insh.
Note 3.-The Clyde
The source of the Clyde is sometimes said to be within 3 miles of that of the Tweed. This refers to the source of Clydesburn, a burn or minor stream which flows into the main body of water where it changes its name from Daer water to River Clyde. 
The mouth of the Clyde is sometimes taken to be at Port Glasgow. This would reduce the total length by 3.3km (2miles) to 165.1km (102.6miles). Its length to Dumbarton Rock is 158.3km (98.4miles)
Note 6.-The Forth
The Forth is measured to the Forth Bridge thus including the length oh the "inner" Firth. Many authorities treat the mouth of the Forth as the boundary of Clackmannanshire and Fife, 1.3km upstream from the Kincardine Bridge, which considerably reduces the river's length. All authorities agree that the Firth of Tay is part of that river and it seems inconsistent to exclude what is a similar stretch of water in the Forth.
Measured to the Kincardine Bridge, the length of the Forth is 112.8km (70.1miles) and the Forth-Teith is 98.4km (61.1 miles)
Note 10.- The Nith  
At low tide, the sea recedes to such an extent that the length of the Nith is extended by 13km to 113.8km (70.7niles), making it the 8th longest river rather than 10th.
Note 12.-The Beauly
The measurement for the Beauly includes 10.9km of the Beauly Firth. Excluding the firth, its length would be 82.4km (51.2miles). Measured to the Kessock Bridge its length would be 93.8km (58.3miles)
Note 13.-The Conon
If the Cromarty Firth is excluded and the measurement taken to the local government boundary (roughly where the River Peffery flows in at low tide), the length of the Conon is 70.3km (43.7miles) and the Conon-Meig's length is 61.3km (38.0miles)
Note 14.- The Galloway Dee  
At low tide, the length of the Nith is extended by 2.9km to 90.9km (56.5miles), making it the 13th longest river rather than the 14th.
Note 18.-The Esk
The last 12.3km of the river is entirely in England. At low tide the length of the river is extended by 11.2km to give a length of 88.2km (54.8miles). This additional length forms part of the boundary between Scotland and England.
Note 20.-The Oykel
Excluding the Dornoch Firth, the length of the Oykel measured to Bonar Bridge is 56.9km (35.3miles). If the main headstream were taken to be River Cassley, the length would be virtually the same, being less than 50metres shorter, which is within the margin of error. The source of the Cassley is on the North side of Conival.
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