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.