Baker—The Fauna of The Lake Winnebago Region. 113 
Lake Winnebago is fed by a number of large streams. Fox River 
enters the northwest end of Lake Butte des Morts and forms a 
channel which extends through this lake, emptying into Lake Win¬ 
nebago at Oshkosh. In fact, these lakes are really widened-out 
portions of the Fox River. Pine Creek and Willow Creek enter 
the western end of Lake Poygon and Wolf River enters the same 
lake from the north. Fond du Lac River, a small stream, enters 
Lake Winnebago at the southern end. The water shed of Lake 
Winnebago covers a wide area in east-central Wisconsin, approxi¬ 
mating 6,200 square miles (see Whitbeck, 1915, pi. iv). The out¬ 
let of Lake Winnebago is by way of the Lower Fox River into 
Green Bay. Just below the dams the river widens to form Little 
Lake Butte des Morts. 
The basin of Lake Winnebago is somewhat platter-shaped, the 
bottom descending more or less abruptly to a depth of three meters 
and then more gradually to five and six meters. The greater part 
of the lake bottom forms a subaqueous plain which varies but 
slightly in contour (see Juday, 1914, pi. 26, and Lake Survey 
map). Subaqueous terraces are rare on the eastern shore but 
common on the western shore, where there are many shallow bays, 
at the points of which bars and shoals extend into deeper water. In 
some places the slopes of these terraces are very steep. The bot¬ 
tom of the lake is of glacial drift of great thickness. 
B. Origin of Lake Winnebago 
Lake Winnebago is the result of changes which occurred during 
the last glacial period—the Late Wisconsin. When the Green 
Bay lobe of the glacier receded it left a morainic dam in the Fox 
River Valley at the present site of the City of Menasha. The lake 
was at first much larger than at present and extended westward 
and southward in the valley now occupied by lakes Butte des 
Morts, Poygon, Winneconne, and a part of the Fox River Valley. 
Fond du Lac was also submerged. Due to readvances of the ice, 
the lake fluctuated in size before reaching its present level. The 
red till, so conspicuous in the wave-cut cliffs near South Asylum 
Bay, and elsewhere, was laid down during one of these advances 
of the Green Bay lobe. 
The glacial outlet was at the present site of Menasha, at the 
northwest corner of the lake, where the bed rock comes to the sur¬ 
face and forms a rock-sill which held the water at different heights 
