2.3. Historical Uses of Our Watersheds In the first section of this manual we talked about how rivers and streams once had abundant populations of fish. Many rivers in our province can not sustain the numbers of fish they once supported. This is primarily the result of the changes people have made to watershed lands and watercourses. Nova Scotia was once covered with an ice sheet a mile thick. As it melted about 12,000 years ago, old river valleys were exposed and new ones were created. Plants, animals, and humans began to inhabit the land as the ice retreated. Gravity pulls water down hill to the sea. Gravity is an accelerating force so, if the water was not slowed by the roughness of the bed and banks of the stream, and the water's internal strength, it would flow faster and faster as it went to the sea. Water flowing down a valley develops characteristic turns and bends as the meandering flow of the water slows its self down. These river valleys were, of course, the best places for humans to settle. Land was cleared without regard for the natural processes. Old trees were cut that held banks in place making the banks erode and causing the river to become shallower and wider. After about 150 years of intensive land use (land clearing, pulp and log drives, dam construction, gravel removal) watercourses, which once had lots of fish, have been and still are being degraded. About twenty years ago people began to get worried about all of these changes to our watercourses. In response to their concerns in the 1970's, many people with good intentions decided to "clean up" our streams. The problem was that they removed everything from the watercourses including logs and dead trees, which were providing important habitat. This is a good example of how work to help a watercourse can backfire! Later in this section we will look in more detail at the impact humans have on watersheds