The Greenbelt is, in many ways, also a water belt. It protects the headwaters, valleys and tributaries of numerous streams and rivers and contains important groundwater reserves, particularly in the Oak Ridges Moraine. Developments and quarries can deplete or contaminate groundwater supplies. Protecting these water sources is one of the most important roles performed by the Greenbelt.
- The Greenbelt’s natural heritage system protects about 535,000 acres of lakes, wetlands, river valleys and forests.
- The Oak Ridges Moraine, a part of the Greenbelt, is a landform unique to southern Ontario.
- It extends 160 kilometres from the Niagara Escarpment in the west to the Trent River system in the east.
- On average, it is 13 kilometres wide and 150 metres deep. It is regarded as the "rain barrel of southern Ontario".