Does the Erie Canal, which connects the Hudson River with Lake Erie make northern New York, southern Quebec, all of New England, all of New Brunswick, and the non-island parts of Nova Scotia an island?
Does the Chicago Sanitary and Ship Canal make all of the eastern part of the US an island?
Does Russia's Unified Deep Water System make ...
It is possible to travel up the Tombigbee River to the Tennessee River. This is because parts of the Tombigbee River are man made.
The key part seems to be the "Divide Cut," a canal linking the Tennessee and Tombigbee Rivers.