Question: The River Swale is a river in Yorkshire, and a major tributary of the River Ure, which itself becomes the River Ouse, emptying into the North Sea via the Humber, a large tidal estuary on the east coast of which country in the Northern region? 

Context paragraphs:
River Foss: The River Foss is an improved river in North Yorkshire, England, and a tributary of the River Ouse.  It rises in the Foss Crooks woods near Oulston reservoir close to the village of Yearsley and runs south through the Vale of York to the Ouse.  The name most likely comes from the Latin word Fossa, meaning ditch and is mentioned in the "Domesday Book".  The York district was settled by Norwegian and Danish people, so parts of the place names could be old Norse.  Referring to the etymological dictionary "Etymologisk ordbog", ISBN  dealing with the common Danish and Norwegian languages – roots of words and the original meaning.  The old Norse word "Fos" (waterfall) meaning impetuous.  The River Foss was dammed, and even though the elevation to the river Ouse is small, a waterfall was formed.  This may have led to the name "Fos", and later changed to Foss.

River Ure: The River Ure is a river in North Yorkshire, England, approximately 74 mi long from its source to the point where it changes name to the River Ouse.  It is the principal river of Wensleydale, which is the only one of the major Dales now named after a village rather than its river.  The old name for the valley was Yoredale after the river that runs through it.

Longest rivers of the United Kingdom: There seems to be little consensus as to the lengths of rivers in published sources, nor much agreement as to what constitutes a river.  Thus the River Ure / River Ouse can be counted as one river system or two rivers.  If it is counted as one, the River Aire / Yorkshire Ouse / Humber system would come fourth in the list, with a combined length of 161 mi and indeed, the River Trent / Humber system would top the list with their combined length of 222 mi (357 km).  Also, the Thames tributary, the River Churn, sourced at "Seven Springs" adds 14 miles to the length of the Thames (from its traditional source at Thames head).  The Churn/Thames' length at 229 mi (369 km) is therefore greater than the Severn’s length - 220 mi (354 km).  Thus, the combined "Churn/Thames" river would top the list.  Sue Owen et al. in their book on Rivers generally restrict the length to the parts that bear the correct name.  Thus the River Nene is quoted at 100 mi , but would be around 5 mi more if the variously named sources were included.  Many of the above lengths are considerably different from Sue Owen's list, some longer and some shorter.

River Esk, North Yorkshire: The River Esk is a river in North Yorkshire, England that empties into the North Sea at Whitby after a course of around 28 mi through the valley of Eskdale, named after the river itself.  The Esk is the only east flowing major river in Yorkshire that flows directly into the North Sea; all other watercourses defined as being major rivers by the Environment Agency, either flow to the North Sea via the River Tees or the Humber estuary.

River Ouse, Yorkshire: The River Ouse ( ) is a river in North Yorkshire, England.  Hydrologically the river is a continuation of the River Ure, and the combined length of the River Ure and River Ouse makes it, at 208 km , the sixth longest river of the United Kingdom and (including the Ure) the longest to flow entirely in one county.  The length of the Ouse alone is about 84 km .

Humber: The Humber is a large tidal estuary on the east coast of Northern England.  It is formed at Trent Falls, Faxfleet, by the confluence of the tidal rivers Ouse and Trent.  From there to the North Sea, it forms part of the boundary between the East Riding of Yorkshire on the north bank and Lincolnshire on the south bank.  Although the Humber is an estuary from the point at which it is formed, many maps show it as the River Humber.

Holgate, North Yorkshire: Holgate is a suburb and unitary authority ward in the City of York.  It is bounded by the River Ouse from Scarborough Bridge to Ouse Acres on its northern boundary.  Its western boundary is formed by one side of Carr Lane and Ouse Acres to the junction of York Road/Acomb Road, which forms part of the southern boundary.  The remainder of the southern boundary follows Moorgate and Holgate Beck to the East Coast Main Line railway which completes the eastern boundary as far as the River Ouse/Scarborough Bridge.

River Nidd: The River Nidd is a tributary of the River Ouse in the English county of North Yorkshire.  In its first few miles it is dammed three times to create Angram Reservoir, Scar House Reservoir and Gouthwaite Reservoir which attract around 150,000 visitors a year.  The Nidd can overflow the reservoirs, flooding the caves in the valley, in which case the river then flows along the normally dry river bed past Lofthouse through to Gouthwaite Reservoir.  The Yorkshire Dales Rivers Trust YDRT has a remit to conserve the ecological condition of the River Nidd from its headwaters to the Humber estuary.  The river gets its name for the Celtic word for "brilliant".

Wouri estuary: The Wouri estuary, or Cameroon estuary is a large tidal estuary in Cameroon where several rivers come together, emptying into the Bight of Biafra.  Douala, the largest city in Cameroon, is at the mouth of the Wouri River where it enters the estuary.  The estuary contains extensive mangrove forests, which are being damaged by pollution and population pressures.

River Swale: The River Swale is a river in Yorkshire, England and a major tributary of the River Ure, which itself becomes the River Ouse, emptying into the North Sea via the Humber Estuary.

Supporting paragraphs: River Swale Humber
Answer: England