The Thames is the longest river entirely in England. At least 20 tributaries flow into it, and it has more than 80 islands.More London travel:
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But the Thames is perhaps best known as the foreground for photographs of London's Houses of Parliament, the reason for Tower Bridge, the front yard of the Tower of London, something that the London Eye is set against, and for cruise boats to float on.
All that touristy stuff.
Yet it is a dramatic waterway. A real, gutsy, characterful and dangerous river. Years ago, I knew the mother of a Thames waterman - a young chap who accidentally fell off the barge he was working on, was immediately sucked down into the powerful, swirling beige waters of the tidal Thames and was only spat back up to the surface days later, a long way down the river. (The moment he vanished, she said, the Weeping Jesus plant in her lounge room started to drop tears, only stopping the moment his body was found. The only time it ever wept.)
The River Thames has an artistic life. Canaletto, J.M.W. Turner, Claude Monet and James Abbott McNeill Whistler all extensively painted it.
It has a literary life. Julius Caesar's writings on his second expedition to Britain in 54BC contain long accounts of the Thames.
Far more contemporarily, it set the theme for Jerome K. Jerome's Three Men in a Boat in 1889 - three chaps on holiday on the river in a small boat. Its smaller reaches were the setting for Ratty, Toad and co to simply mess about in boats in Kenneth Grahame's The Wind in the Willows, which he wrote in 1908, and Charles Dickens thoroughly described it, and the lives of those working on it, in Our Mutual Friend, which he finished in 1865. And many of these books may suit Ben McCann - a sixth generation Thames waterman.
"I read books about London and books about boats," he says as he skippers the tourist cruise boat Millennium Dawn between the London Eye and Greenwich. "We watermen are very proud of our history - and proud of the history of London and the Thames."
The first bridge was built over the Thames in AD43, says Mr McCann, and it was the only bridge until the 1700s. Westminster Bridge was built in 1746.
Today there are 29 bridges over the tidal Thames, and 75 across its non-tidal reaches, but previously people had to use watermen to cross the river - they'd wait on the bank, and the river workers took them along and across it. The human history of the River Thames is strong and long, dating back to Neolithic times, but it is the natural, environmental, nothing-to-do-with-you life of the tidal Thames that I am particularly interested in. For the Thames has a massive, natural life and has a great influence on the North Sea. Its tide can rise 8m and run at more than 11km/h.
The average human walking speed is 5km/h and a good, strong paddler in a fast sea kayak can maintain a speed of perhaps 9km/h.
But the river's first path wasn't through here at all. For nearly 60 million years until the great ice sheet of the Quaternary Ice Age formed, some 450,000 years ago, the Thames flowed through what is now Oxfordshire, then bore north-east to drain into the sea near Ipswich. But the ice dammed the river in Hertfordshire, creating ice lakes which eventually flooded, with the thaw, pretty much on to the river's present day course to and through London.
For 89km from Teddington Lock to the mouth of the Thames Estuary, the North Sea brings its influence. And for some of this, the Thames Path follows the bank.
The Thames Path is a 294km National Trail footpath, running from the Thames Flood Barrier at Woolwich, 7.2km downstream from Greenwich, where it is 450m wide, to Kemble in Gloucestershire.
But I am particularly interested in the tidal Thames and today I am just tackling the 12km leg from Greenwich to the London Eye.
I easily take public transport to this favourite place - home of Greenwich Mean Time, the Royal Observatory, the National Maritime Museum, and the only surviving British tea clipper, Cutty Sark, which was launched in 1869 and is under restoration.
And I easily pick up the Thames Path, which leads through Deptford, Rotherhithe and Bermondsey. After which, I look across the water to the huge development of Canary Wharf, with industrial riverside buildings - many of which were primarily used for trade to the Canary Islands - being converted into accommodation.
I have previously passed this on Millennium Dawn's river trip from the London Eye to Greenwich, Ben McCann commenting that this development has taken 30 years so far, with 30 to go.
All well and good, but I keep my eye on the water, brown as the result of up to an estimated 300,000 tonnes of sediment a year, not pollution.
The dawn of the flushing toilet might once have turned this into a sewer but river authorities say that the Thames today is cleaner that at any time in the 20th century, and recognised as one of the cleanest metropolitan estuaries in Europe.
And on my day walk, I spot a raft of birdlife, most commonly cormorants, oystercatchers, mallards, shelducks and those bulky and hook-beaked herring gulls, but also herons and a crested grebe.
Under the surface, the tidal Thames has some 115 species of fish, including thin-lipped mullet, flounder, smelt and perch, and is rich in invertebrates. It is reported that colonies of short- snouted seahorses have also recently been found in the river.More river travel:
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Soon I am past Tower Bridge, City Hall (which looks like a motorcyclist's helmet) and at the London Eye on the South Bank.
But I carry on, still caught by the tide, through the riverside gardens of the Albert Embankment, Lambeth, and over the Vauxhall Bridge turning left towards Pimlico.
At the Westminster Boating Centre in Grosvenor Road, three sailing dinghies are moored, like ducks in a row. And it is here I have to leave the river, peeling off towards my hotel, but with a vague dream. The whole 294km of the Thames Path National Trail? A transect through landscape and history.Now, that's an interesting thought.