Britain's rivers are in crisis, with only 14% of them deemed to be in a good ecological state. Chalk streams are particularly vulnerable, as so much is taken out of them for use in our water supplies. Pollution from sewage and agricultural run-off only add to the problem. In this programme Tom Heap takes a canoe trip along a waterway he knows well, the River Cam, to see for himself what's going on. He talks to environmental groups and local people, and asks whether the rapid expansion of homes and businesses in the area can sustainably continue in such a water-stressed region. He concludes that urgent action is needed if rivers like the Cam are not to run dry. Producer: Emma Campbell