Old Father Thames

The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn.

The river rises at Thames Head in Gloucestershire, and flows into the North Sea near Tilbury, Essex and Gravesend, Kent, via the Thames Estuary. From the west it flows through Oxford (where it is sometimes called the Isis), Reading, Henley-on-Thames and Windsor. The Thames also drains the whole of Greater London.

In August 2022, the source of the river moved five miles to beyond Somerford Keynes due to the heatwave in July 2022.

The lower reaches of the river are called the Tideway, derived from its long tidal reach up to Teddington Lock. Its tidal section includes most of its London stretch and has a rise and fall of . From Oxford to the Estuary the Thames drops by 55 metres. Running through some of the drier parts of mainland Britain and heavily abstracted for drinking water, the Thames' discharge is low considering its length and breadth: the Severn has a discharge almost twice as large on average despite having a smaller drainage basin. In Scotland, the Tay achieves more than double the Thames' average discharge from a drainage basin that is 60% smaller.

Along its course are 45 navigation locks with accompanying weirs. Its catchment area covers a large part of south-eastern and a small part of western England; the river is fed by at least 50 named tributaries. The river contains over 80 islands. With its waters varying from freshwater to almost seawater, the Thames supports a variety of wildlife and has a number of adjoining Sites of Special Scientific Interest, with the largest being in the North Kent Marshes and covering .

Etymology

According to Mallory and Adams, the Thames, from Middle English ''Temese'', is derived from the Brittonic name for the river, ''Tamesas'' (from *''tamēssa''),Mallory, J.P. and D.Q. Adams (1947). ''The Encyclopedia of Indo-European Culture''. London: Fitzroy and Dearborn. p. 147. recorded in Latin as ''Tamesis'' and yielding modern Welsh ''Tafwys'' "Thames". The name may have meant "dark" and can be compared to other cognates such as Russian темно ( Proto-Slavic *''tĭmĭnŭ''), Lithuanian ''tamsi'' "dark", Latvian ''tumsa'' "darkness", Sanskrit '' tamas'' and Welsh ''tywyll'' "darkness" and Middle Irish ''teimen'' "dark grey". The origin is shared by many other river names in Britain, such as the River Tamar at the border of Devon and Cornwall, several rivers named Tame in the Midlands and North Yorkshire, the Tavy on Dartmoor, the Team of the North East, the Teifi and Teme of Wales, the Teviot in the Scottish Borders and a Thames tributary the Thame.

Kenneth H. Jackson proposed that the name of the Thames is not Indo-European (and of unknown meaning), while Peter Kitson suggested that it is Indo-European but originated before the Britons and has a name indicating "muddiness" from a root ''*tā-'', 'melt'.

Indirect evidence for the antiquity of the name 'Thames' is provided by a Roman potsherd found at Oxford, bearing the inscription ''Tamesubugus fecit'' (Tamesubugus made his. It is believed that Tamesubugus' name was derived from that of the river. Tamese was referred to as a place, not a river in the Ravenna Cosmography (c. AD 700).

The river's name has always been pronounced with a simple ''t'' /t/; the Middle English spelling was typically ''Temese'' and the Brittonic form ''Tamesis''. A similar spelling from 1210, "Tamisiam" (the accusative case of "Tamisia", see Kingston upon Thames#Early history), is found in the Magna Carta.

The Thames through Oxford is sometimes called the Isis. Historically, and especially in Victorian times, gazetteers and cartographers insisted that the entire river was correctly named the Isis from its source down to Dorchester on Thames and that only from this point, where the river meets the Thame and becomes the "Thame-isis" (supposedly subsequently abbreviated to Thames) should it be so called. Ordnance Survey maps still label the Thames as "River Thames or Isis" down to Dorchester. Since the early 20th century this distinction has been lost in common usage outside of Oxford, and some historians suggest the name ''Isis'' is nothing more than a truncation of ''Tamesis'', the Latin name for the Thames. Sculptures titled ''Tamesis'' and '' Isis'' by Anne Seymour Damer can be found on the bridge at Henley-on-Thames, Oxfordshire (the original terracotta and plaster models were exhibited at the Royal Academy, London, in 1785. They are now on show at the River and Rowing Museum in Henley).

Richard Coates suggests that while the river was as a whole called the Thames, part of it, where it was too wide to ford, was called *''(p)lowonida''. This gave the name to a settlement on its banks, which became known as Londinium, from the Indo-European roots *''pleu-'' "flow" and *''-nedi'' "river" meaning something like the flowing river or the wide flowing unfordable river.

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 non-administrative use, the river's name is used in those of Thames Valley University, Thames Water, Thames Television, publishing company Thames & Hudson, Thameslink (north–south rail service passing through central London) and