A 21-year study of over 2,300 rivers in Britain measured the presence of clean-river invertebrates - a yardstick for river health – and found they are the cleanest they've been in over two decades. During the days of heavy industry and poor sewage treatment,
had declined considerably, but now appear to be making a comeback, say scholars
from Cardiff University
Dr. Ian Vaughan and Professor Steve Ormerod from the University's School of Biosciences analyzed changes in the occurrence and spread of insects, snails and other mini-beasts from major rivers between 1991 and 2011. The researchers then asked whether water quality, temperature or river flow best explained the biological changes they observed.