Pollution control efforts seem to be working on Britain’s urban rivers:

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.

They examined the presence and spread of 78 organisms – including insects, snails and others – and claim many are making a comeback following decline.

The scientists say the improvements are largely due to reductions in pollution levels.

I learned of this via the always helpful Circle of Blue’s The Stream.