The source is usually given as Thames Head, which is about one mile north of Kemble, near Lechlade and Circencester in Gloucestershire, England.
The Thames rises in the Cotswolds at Trewsbury Mead, 108.5 metres (356 feet) above sea level, though you have to use your imagination to a fair degree as for most of the year there is no sign of water. The source is marked by a solitary stone with the inscription:
The Conservation of the River Thames
1857 -1974
This Stone was Placed Here to Mark the
Source of the River Thames
However, the source of the Thames is disputed. The Environment Agency (and its predecessors), the Ordnance Survey and most authorities now accept that Trewsbury Mead is the source but others hold that the true source of the Thames is at Seven Springs, some eleven miles further north and a little to the south of Cheltenham. Officially this is the source of the River Churn, a tributary of the Thames that joins at Cricklade. The stream that flows from Trewsbury Mead has been called the Thames throughout recorded history. Similarly, the river from Seven Springs has been called the Churn from earliest times, giving rise to the names of the villages of North and South Cerney and to Cirencester (Corinium) itself. But this is an argument that can never be fully settled.
Please see the related link below for further information.
The Thames begins near Cirencester. The actual source is disputed by various experts & agencies. The traditional belief is Thames Head, others hold that it is Trewsbury Mead, or Seven Springs. As these three localities all fall within a five-mile radius, it is probably accurate enough to just say Cirencester.
Thames Head, Gloucestershire.
It rises at Thames Head in Gloucestershire, the Cotswold Hills
That would be the River Thames.
The River Thames is the major river through London, cutting right through the middle of the city. There are many other rivers in London, such as the River Lee (or Lea) and the River Brent.
The river Thames (pronounced temz)
London is situated on the River Thames (pronounced 'temz'.
Thames River
The Thames flows through London.
The River Thames has multiple confluences. One such is the confluence of the River Thames and the River Darent at Dartford.
The river Thames.
The river Thames is in England.
River Thames.
The River Thames does not have a delta.