During my early fieldwork (1967-77) by helicopter, float planes and boats in Northern Manitoba for the Canada Land Inventory Survey, beavers, beaver dams and ponds were certainly a recognizable part of the landscape, but not in unuasal abundance. When I revisited the same areas in 2004 using for the first time Google Earth I was struck by seeing so many dams, pond and lodges, where I had never seen them 40 years earlier. I started a series of post on the Google Earth forum- "beavers, beavers, everywhere..."
The combination of images below gives an example that struck my curiosity. No signs of beaver dams, ponds and wetlands can be seen in 1967- grey toned aerial photos, which together form a stereo pair. The right green image is the 2004 Satellite image. The flow in the stream which certainly did exist in 1967, is now completely managed by the beavers through an abundance of dams. The former 'glacial lake' island near A shows the former shorelines of the lake when it receded. A large forest, wildland fire swept through the area, exposing the white limestone bedrock (B) and glacial lake strand lines. In the bottomlands, near C, small spring fed ponds typical of this karst landscape.