Urban rivers throughout England and Wales have improved dramatically in water quality and wildlife over the last 20 years. That's the conclusion of one the largest studies of national trends in river health ever undertaken. After decades of pollution, typically from poorly treated sewage and industrial waste, rivers in or near Britain's major urban areas are regaining insects such as mayflies and stoneflies that are typical of fast-flowing, oxygen-rich waters. The range of invertebrates found has also increased, on average, by around 20%. Researchers from the School of Biosciences carried out an independent analysis of data supplied by the Environment Agency using almost 50,000 samples from thousands of rural and urban locations.