14 ILLINOIS BIOLOGICAL MONOGRAPHS [14 



low, swampy banks in a bed that is made up largely of soft muck. It varies 

 in width from twelve to nearly fifty feet during the early summer, but the 

 end of the warm weather often finds the stream reduced nearly to a mini- 

 mum. A number of gravel areas occur and here riffles afford local swift 

 water habitats, characterized by typical swift water species of fishes. 

 Plant growth is abundant and during the late summer the stream becomes 

 practically choked with thick beds of Potamogeton, Nymphaea and 

 limnophilous species of filamentous algae, while areas of Ceratophyllum 

 occur particularly in regions of entering springs. The stream has a total 

 length within the county of approximately sixteen miles, and has no 

 tributary streams of consequence. It enters Rock river three quarters of 

 a mile west of the county line, the closest approach of Rock river to 

 Waukesha county. 



The Oconomowoc river drains a long, torturous, but rather narrow 

 valley lying south and east of the Ashippun drainage. Serving, as it does, 

 as a connection between a large number of lakes, and as it is a river of 

 considerable size, it affords an important fishway. Innumerable streams 

 and creeks, all of them spring fed, are tributary to it in the northern 

 portion of its course, of which the Little Oconomowoc and Mason creek 

 are the largest. In its northern reaches the river flows through a low, 

 swampy, spring-fed country of loose black muck, varied with areas of 

 gravel and sand. For the most part it is slow and sluggish, but there are 

 occasional regions of considerable drop, where swift water habitats pre- 

 dominate. Such areas are plantless, while in the sluggish regions Potamoge- 

 ton sp., Elodea canadensis, Nymphaea advena, Chara sp., and Vallisneria 

 spiralis occur in considerable abundance, but not thick enough to choke 

 the river. In stagnant backwaters local regions of Lemna minor are found. 

 Important as is the river as a fishway, its value is greatly reduced by the 

 presence of six dams — Monches, North Lake, Okauchee Lake, Oconomo- 

 woc Lake, Fowler Lake, and the outlet of Lac La Belle. These dams afford 

 a downstream passage for many species of fish, but are impassible barriers 

 in upstream migrations — particularly the spring and fall migrations of the 

 pickerel (Esox lucius), suckers of various species, and cisco (Leucichthys 

 artedi). As the river flows into Rock river six miles west of Lac La Belle, 

 the river is a constant source of supply of valuable game fish to the Rock 

 river, while this river can contribute nothing at all to the Oconomowoc 

 river above the outlet of Lac La Belle. It must therefore be considered as 

 an important fish tributary to the Rock river. 



The Bark river cuts a diagonal from the northeast to the southwest 

 just northwest of the center of the county, draining a large area lying north 

 of the main ridge of the kettle moraine. Its course is through a rich farming 

 country, and it is not until it approaches the western limits of the county 

 that it encounters large swamp areas. This is due to the fact that the greater 



