The River Thames ( ) is a river that flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom, after the River Severn. While it is best known for flowing through :London, the river also flows alongside other towns and cities, including Oxford, Reading, Henley-on-Thames, and Windsor.
The river gives its name to three informal areas: the Thames Valley, a region of England around the river between Oxford and west London; the Thames Gateway; and the greatly overlapping Thames Estuary around the tidal Thames to the east of London and including the waterway itself. Thames Valley Police is a formal body that takes its name from the river, covering three counties. In an alternative name, derived from its long tidal reach up to Teddington Lock in south west London, the lower reaches of the river are called the Tideway.
The administrative powers of the Thames Conservancy have been taken on with modifications by the Environment Agency and, in respect of the Tideway part of the river, such powers are split between the agency and the Port of London Authority. In non-administrative use, stemming directly from the river and its name are Thames Valley University, Thames Water, Thames Television productions, Thames & Hudson publishing, Thameslink (north-south railways passing through central London), and South Thames College. Historic entities include the Thames Ironworks and Shipbuilding Company.
Two broad canals link the river to other river basins: the Kennet and Avon Canal (Reading to Bath) and the Grand Union Canal (London to The Midlands). The Grand Union effectively bypassed the earlier, narrow and winding Oxford canal which also remains open as a popular scenic recreational route. Three further cross-basin canals are disused but are in various stages of reconstruction: the Thames and Severn Canal (via Stroud), which operated until 1927 (to the west coast of England), the Wey and Arun Canal to Littlehampton, which operated until 1871 (to the south coast), and the Wilts and Berks Canal.
Rowing and sailing clubs are common along the Thames, which is navigable to such vessels. Kayaking and canoeing also take place. Major annual events include the Henley Royal Regatta and The Boat Race, while the Thames has been used during two Summer Olympic Games: 1908 (rowing);1948 (rowing and canoeing). Safe headwaters and reaches are a summer venue for organised swimming, which is prohibited on safety grounds in a stretch centred on Central London. Non-Olympic watersports with a lesser presence include skiffing and punting.