Wild Swimming Becoming a Popular Pastime

Wild swimming, a growing trend, involves swimming in open water. Its popularity has been partly attributed to comedian David Walliams, who swam the English Channel for charity. He is now planning to swim the Thames. Wild swimming groups are forming to support newcomers. The water quality in rivers and lakes is better than it has been in a century, making it an ideal time to try wild swimming. Beginners are encouraged to start with friends and use online resources. Historically, wild swimming was popular before WWII, but despite cleaner waters, it is less common today.

How has the cleanliness of rivers and lakes changed in the last 100 years?

What historical context is provided about wild swimming before the Second World War?