March, 1963 



Larimore & Smith: Fishes of Champaign County 



315 



nel. They consist of a long open ditch, 

 flowing smoothly over a substrate of clay, 

 silt, or loam. They lack aquatic vegeta- 

 tion but are bordered by grasses, herbs, 

 and shrubs. Although they include oc- 

 casional water pockets that could be 

 termed pools, and occasional shallow areas 

 where there is an accumulation of sand 

 and gravel suggesting riffles, their distri- 

 bution of fishes is relatively uniform 

 throughout. These long open ditches may 

 partially dry up if water flow ceases dur- 

 ing the summer months. Their small size, 

 instability of flow, and lack of shade pro- 

 duce a highly unstable aquatic environ- 

 ment. 



Large Greeks. — The streams we 

 classify as large creeks are formed by the 

 confluence of the rivulets and small creeks. 

 The water contributed by the network of 

 tributaries is of such volume that flow is 

 continuous throughout most years, al- 

 though the actual volume may fluctuate 

 drastically from wet to dry seasons. 

 Typically, the large creeks consist of al- 

 ternating pools, shallow stretches, and rif- 

 fles (frontispiece). They contain a greater 



variety of habitats than do rivulets and 

 small creeks. The frequency of occurrence 

 of riffles depends upon the distribution of 

 glacial drift materials, the extent of 

 dredging, and the stream gradient. Some 

 of the large creeks in Champaign County 

 have been dredged ; they now have straight 

 rather than meandering courses, a mo- 

 notonous sameness of environment, and 

 nearly uniform depth, fig. 8. 



In the large creeks, riffles over sand 

 and fine gravel are usually without aquat- 

 ic vegetation ; those over gravel and small 

 boulders have some attached algae. Some 

 pools are shallow and have a moderate 

 flow over clay, sand, and silt ; they have 

 a variety of aquatic vegetation. Other 

 pools are quiet and deep, having been 

 formed by obstructions or unusual erosion 

 of the bottom materials ; they have ac- 

 cumulations of silt and only marginal veg- 

 etation. Long, shallow pools make up 

 large proportions of most of the Cham- 

 paign County streams we have classified as 

 large creeks, fig. 11. 



Small Rivers. — The largest streams 

 in the county, hardly larger than creeks 



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Fig. 8. — The Kaskaskia River southwest of Parkville. This stream, dredged from time to 

 time, illustrates one of the large creek habitats found in Champaign County. Modification of 

 this creek resulted in an unusual amount of sand in the stream bed. 



