16 ILLINOIS BIOLOGICAL MONOGRAPHS [16 



movements in both directions. Its chief tributary is the Pewaukee river, 

 the outlet of Pewaukee lake. 



The Menomonee river rises in Washington county just north of the 

 northeastern corner of Waukesha county, through which it flows in a 

 northeasterly direction. It is a very small stream, flowing almost entirely 

 through limestone (Niagara) formation. Its bed is a mass of limestone 

 rocks which afford no footing for plant growth, so that both plants and 

 fishes are few. Occasional areas of swamplands bound the river as it 

 progresses eastward, and here there is an abundance of minnow life very 

 different in composition from the other river systems, none of which are 

 tributary to Lake Michigan into which the Menomonee empties via a short 

 connection with the Milwaukee river within the city limits of Milwaukee. 

 Within Waukesha county it has but one tributary stream, the Little 

 Menomonee, which joins it from the north. Within the county there is no 

 place at which the river is large enough to offer game fish habitation, but 

 it is of importance to the fish fauna of the county, introducing as it does a 

 number of species not found in the western part of the state — the Rock 

 river and the Illinois river tributaries. 



As has already been mentioned, the vast majority of the lakes of the 

 county fall into a series of chains with river connections. There remain, 

 however, a great number of small lakes, almost too many to count, unless 

 one designates a minimum size as to what constitutes a "lake" — which 

 lie outside of these river systems, and which have neither inlet nor outlet. 

 The larger of these I have already listed. However, many small lakes 

 abound. North of Okauchee lake lies a series of lakes, some seventeen in 

 number, all containing fish life, which are known as the Skidmore ponds, 

 and similar areas are found scattered over the county. All of these are 

 relatively small in size and all occupy depressions in morainic areas. Most 

 of them are quite deep — much deeper than their size would lead one to 

 infer — and all are spring fed, relying upon springs and surface drainage 

 and rainfall as their source of water supply. Many of these lakes lie in 

 swamp areas, and are the last remnants of former lakes of considerable 

 size, though of little depth. In many cases the former shoreline of these 

 old bodies of water is plainly visible, being indicated by gravel terraces. 



Although all of the lakes are of practically the same age, the smaller 

 ones in many cases already show marked indications of old age. The 

 encroachment of the shore vegetation upon the lake is very evident, as 

 shown in the photograph of Laura Lake, while the old lake bed and an 

 island which is now a point is clearly shown in Plate I. The larger lakes, 

 naturally, show less evidence of ageing, though of course the process is 

 going steadily on. 



The water of all of the larger lakes is remarkable for its purity and 

 clearness, and none of the lakes within the county suffer from the pollution 



