River Swim
Kim, however, is a veteran and there are stretches of the river which are fantastical and make me think of Huckleberry and Jim going down the Mississippi River, pulled by the water flow. We always swim West of Teddington Lock, where the river is fresh-water from a source near Oxford vs. East of the lock which is salt-water tidal (and passes through the center of London). On cleanliness, the Thames was declared a dead river in 1981. Today, there are otters and a dolphin sited only yesterday; there is talk of the ancient salmon-runs coming back.
In winter, the Thames can go as low as 1C requiring wetsuits, gloves, booties and a thermal hat ("skins", the Brits call it). We always swim in two's otherwise dangerous from cold or boats (rowers, propeller, sometimes barges). Spring and summertime the temps will reach 16-18C. Whenever it rains we have to be extra careful about the current which can run 2-3 knots and impossible to swim against.
In short, the river has a personality that is worth getting to know.