Look what’s struggling to swim the Thames now… trout

http://junkscience.com/2012/03/23/look-whats-struggling-to-swim-the-thames-now-trout
Previously filthy watercourses are now teeming with fish, a new book reveals Increasing numbers of rivers in towns and cities in Britain are now so clean that anglers are fly-fishing in them for trout and grayling, which are specialised clean-water species, a new book says.