Cardiff University: Urban rivers cleanest for 20 years
2 June 2014 Last updated at 11:12 BST
Britain's urban rivers are the cleanest they have been for more than two decades, a study has found.
More than 2,300 river sites in England and Wales were analysed between 1991 and 2011 by Cardiff University.
Steve Ormerod, professor of ecology at the university's school of biosciences and one of the co-authors, told BBC Radio Wales that by fixing the pollution problem, it was helping to offset some of the adverse effects of climate change.