I grew up in west
central Minnesota, 3 miles from the Mississippi/Hudson Bay continental
divide (which is only about 1080 feet above sea level there). Check
out a MN/SD map and look at the Lake Traverse/Bigstone Lake boundary.
I remember as a high school kid cross country skiing over the Mississippi
where it exits Lake Itasca, it's only about 3 feet wide there. Just
some ideas you might want to ruminate over for the documentary.