The River Thames rises in Gloucestershire
on the slopes of the Cotswolds
. Depending on choice, it either originates at Thames Head near Cirencester or at Seven Springs, 3.5 miles south of Cheltenham
. The length of the river from its head to the Nore is 209 miles. At London Bridge
, the width is about 900 feet. At the Nore, it is more than five miles. The river shows the effects of tides as far upstream as Teddington in SW London
. The river is navigable to within a few miles of its source.
] Over it course, the Thames separates the counties of Gloucestershire, Oxfordshire, Buckinghamshire, Middlesex, and Essex from Wiltshire, Berkshire, Surrey, and Kent.