grows significantly in size from at the Portage to about at USGS gage 004073500 at Berlin, where the average flow is about . The river discharge would grow at nearly the same proportions. Thus the Upper Fox grows from a small stream to a small river over its course. At Big Lake Butte des Morts it is joined from the north by flow from the Wolf River through Lake Poygan. The drainage area of Wolf River is more than twice the size of the drainage area of the Fox. But this extra flow joins the Fox only after it reaches the Lake Winnebago Pool. The river channel is characterized by sand, silt and organic material. The channel, which ranges from , is shallow and generally widens and deepens as it approaches Lake Winnebago. Lower Fox The lower Fox River flows from the natural impoundment of Lake Winnebago to Lake Michigan. It extends about 39 river miles (63 km) from Menasha at the head of Lake Winnebago to Lake Michigan, falling from about elevation , msl at Winnebago to , msl at Green Bay. The reach has a very steep and changing grade. While the hydraulic gradient averages about 4 feet per mile (0.75 m/km), there are very large falls at (using the original French nomenclature) La Grand Kaukilin (Kaukauna), La Petite Chute (Little Chute) and La Grand Chute (Appleton). The total drop of these falls is approximately the same as Niagara Falls, although over a much longer stretch. There are no major tributaries. Thus the river discharge is nearly constant, averaging about at USGS gage 040851385 at Green Bay. History prior to modifications The reach served as a highway for Native American peoples and, later, European explorers and fur traders both indigenous and European. They used the Fox and Wisconsin rivers as a primary highway between the Great Lakes and Mississippi River. In fact, it was the most heavily traveled of all the portages between the Great Lakes and Mississippi watersheds. From the Portage, one could travel north to nearly Lake Superior along the Upper Wisconsin River, west to the Mississippi along the Lower Wisconsin River, or northeast along the Fox River to Lake Michigan. Other watersheds, such as the Wolf River to north central Wisconsin or the Rock River to the Illinois country, were within easy distance. In the 17th century the area was dominated by a number of