Raw sewage overflowing from an access cover (manhole) for a public sewer, in Oxfordshire, UK. The sewage is flowing down a footpath to reach a chalk stream (not seen). This pollution is a threat to the ecology of the stream, being toxic to the fish, waterfowl and other wildlife and plants. Such overflows have to be reported to the UK Environment Agency. This overflow was caused by tree roots that broke into the sewer pipe further downstream. Urban expansion has led to problems with the maintenance of old sewer pipes and drainage systems.