The Thames has always been all things to all people, including those who choose to immerse themselves in it.

Caitlin Davies’s new book, Downstream, is a colourful history of Thames swimmers.

The cast of characters, ranging from extreme sportsmen to even more extreme eccentrics, is huge.

All life is here, and it is life.

One striking fact is the absence of drowning. “The Thames,” the author concludes, “has always been, and always will be, a swimmer’s friend.”

Swimmers have enjoyed every stretch of the river (bar the first fewmiles at Kemble, so shallow that they barely justify the use of wellies). But a striking feature of the saga is the number of swimmers who have been brave enough, or self-challenging enough, or mad enough, to swim in the Estuary off Southend.

Southend pier is the endpoint for those who attempt the feat of swimming the entire length of the Thames, and as Caitlln reveals, the waters off the pier pack a few nasty surprises – at least for those who don’t not know Southend.

One of the funniest stories in the book concerns Charlie Wittmack, an American extreme sportsman who swam along the Thames in 2010. Most of the journey was pretty effortless, until the pier hove into view. First Charlie was done over by a shoal of chavvy Essex jellyfish, then he found the tides making merry hell of his schedule. Rather wetly (in more ways than one, some might say), he made for the shore, to consult his GPS.

While he stood there, the tide suddenly went out. The bold swimmer found himself stuck in the mud, and had to call for the rescue services.

Local swimmers have usually had more success, starting with the gung-ho sportsmen of the Southend Swimming Club, founded in 1894. The club specialised in swimming to the pierhead, and then back again along the other side. One of the club’s members became a national swimming hero.

Norman Leslie Derham had come to live in Southend in 1921. Derham’s life outside the water sounds as colourful as his life in it. He had worked variously as a Royal Flying Corps pilot, pig farmer, brass bed manufacturer and banana distributor.

But swimming was the real focus of his life.

In 1926, Derham set out to beat the world record time for a Channel swim, which was then held by an American. Before that, however, he set out on another endeavour, the first swim across the Thames Estuary from Southend to Sheerness. His initial attempt failed, not least to an unexpected problem. “Several miles from the shore,” he told a local reporter, “a large porpoise rose to the surface beneath me, lifting me completely out of the water.”

Excuses, excuses.

On another occasion, a passing Belgian steamer opened her bilges on top of him, making him ill for the next three weeks. But Derham perservered, and on September 16 1926 he succeeded in his bid to swim the Channel in record time, firmly establishing himself as a national hero.

Everymile of the Thames has its own stories of swimmers to tell, and Catilin Davies tells them with relish.

The author, who lives in London, was first attracted to the subject while researching a previous book, on the famous Hampstead swimming ponds.

She stumbled across the story of Agnes Beckwith, a Victorian teenager who specialised in jumping off boats fully clothed and swimming long distances in the Thames. Agnes beat a number of records established by men, although the press tended to concentrate more on the pink frilly costumes she wore.

“One thing led to another and I realised that there was a book to be written about Thames swimmers,” Caitlin says. She has trawled the river from source to mouth in search of stories, travelling 15,000 miles in the process. Of course, as is only right, she has also entered the water at a few sites.

“I’m a fair weather swimmer,” she says. “But I did enjoy a few swims, though nothing you could call heroic.”

At least it is possible to say that Downstream has been swum as well as written.

  • Downstream is published by Aurum Press at £16.99 ISBN 978 1 78131 1196