That's interesting. I didn't know the river went as far north as Green Bay. I grew up 40 miles south of the Wisconsin state line. Nice to hear there are actually fish in it today. Wasn't anything in it you could actually eat back then, even the meat of the cat fish was stained green from the chemicals. Only thing that seemed healthy were the snapping turtles but they are air breathers so . . .
Well, there are two Fox Rivers. One starts up in some marshes up north of Portage WI, wanders into Lake Winnebago, comes out of Winnebago running North and debouches into the Bay of Green Bay. The other Fox River starts in SE WI and runs a couple hundred miles into Illinois.
The Fox River that runs into Green Bay was an important water route during first European exploration, the fur trade, and early water born transportation. There is a short portage at, of all places, Portage. In early times this portage was controlled by the natives of the area. Prior to rail road expansion, a short canal was constructed to connect the Fox River to the Wisconsin River which runs into the Mississippi River at Prairie Du Chien, and thence to the Gulf of Mexico to the South or the source of the Mississippi upstream to the area of Grand Rapids, MN.
Too have seen the Fox River when it was first seen and documented by early explorers would have been marvelous, and a regret I will alway have that I could not see the series of rapids the Fox descends as it flows over the Niagara escarpment. Yes, the same Niagara escarpment as the famous Niagara Falls. This escarpment extends from somewhere in Illinois across Wisconsin, occasionally exposed by glaciation, gouged out by glaciers after Door County WI and lies under Lake Michigan, only to be exposed again at the Falls. How far it extends after the Falls I don't know.
Geology was one of the things I paid attention to in college.