There is a chance that hazy stretches at the top of streams did not exist in presettlement times, but that rain water seeped through swampy forest for some distance before it came above ground as a distinct stream. When the land was cleared for farming, ditches (later filled in and completely obliterated) were dug through the wet areas to prepare for field crops. Frequently where the topography was only slightly rolling, ditches would be dug along field boundaries rather than the absolutely lowest location.
Some stretches have been lost by the heavy hand of man, especially where major transportation nodes are located. The construction of Highway 401, and to some extent the rail lines, obliterated any stream in their way. The upper bits of Mud Creek and the piece of Yellow Creek just west of Yonge Street were obliterated by TTC yards.
Other streams we show as “lost” coming out from the Lake Iroquois Shoreline, such as the lower parts of Wychwood Creek, usually considered the top of Taddle Creek and Mashquoteh Creek may not have existed above ground. The possibility is that when Lake Iroquois drained out, these streams flowed out onto and went underground into the sands and gravels of the Iroquois beach, later to feed several nearby streams. Only larger streams, such as Garrison Creek and Castle Frank Brook, would have enough flow at flood conditions to cut a valley through the Iroquois terrace to the lake or the Don River.