This is a journey through the Quabbin watershed, from north to south. The Swift River, Hop Brook and other streams flow into the Quabbin to provide water for Metropolitan Boston. Four towns were taken in the 1920's and 30's for this purpose displacing thousands. In the process, an "accidental wilderness" was created. Here, on what was farm land just 100 years ago, the forest filters and protects the water and a wide variety of wildlife, and there is little human intrusion.