A new by-law bans swimming in the River Thames without prior permission from the Port of London Authority.
From Sunday, prior written permission will be needed to swim anywhere in the Thames between Crossness in east London and Putney Bridge in south-west London.
The BBC reports there has been an increased interest in river swimming since comedian David Walliams swam the length of the Thames from Gloucestershire to Westminster Bridge in central London last year, a distance of 140 miles.
The PLA said the river is dangerous, with tides, strong currents, and whirlpools and the ban is needed because it had a responsibility for the safety of all river users.
