River Thames to the strong current of the river, but also other river users. Organised swimming events take place at various points generally upstream of Hampton Court, including Windsor, Marlow and Henley. In 2011 comedian David Walliams swam the from Lechlade to Westminster Bridge and raised over £1 million for charity. In non-tidal stretches swimming was, and still is, a leisure and fitness activity among experienced swimmers where safe, deeper outer channels are used in times of low stream. A Thames meander is a long-distance journey over all or part of the Thames by running, swimming or using any of the above
River Thames high concentrations can be toxic to marine life and humans. Sixty sediment cores of 1 m in depth, spanning the entire tidal River Thames, between Brentford and the Isle of Grain have been analysed for total Hg. The sediment records show a clear rise and fall of Hg pollution through history. Mercury concentrations in the River Thames decrease downstream from London to the outer Estuary with the total Hg levels ranging from 0.01 to 12.07 mg/kg, giving a mean of 2.10 mg/kg which is higher than many other UK and European river estuaries. The highest amount of sedimentary-hosted Hg pollution