xliv FISHES OF ILLINOIS 



ever, is in any case but slight, the lake being, indeed, not infre- 

 quently the recipient of river water. Spoon River still pours a 

 sluggish but constant stream into the river, but save for a 

 waterbloom of livid green (Euglena) its waters yield but little 

 plankton. Thus, of all the wide area contributing to the plankton 

 of the channel at high water there now remain only Thompson's 

 and Quiver lakes and Spoon River, each much diminished in 

 volume, but all diversified in character. 



" Returning now to the river itself we find a gently sloping 

 bank of black mud, baked and cracked by the sun's heat, ex- 

 tending towards the softer deposit at the water's margin. A low 

 growth of grasses, sedges, and weeds springs up as the water 

 recedes. The river margin does not often have much aquatic 

 vegetation. In low- water years, such as 1894 and 1895, a con- 

 siderable fringe is formed along the shore, but this is quickly 

 cleaned out on the seining grounds, which occupy a large part of 

 the shore, as soon as the fishing season opens in July. In years 

 of normal high-water the vegetation rarely gets much of a 

 foothold along the shores, even at low-water stages. Save for 

 the few sandy banks where springs abound, such as those 

 below Havana along the eastern bluff, there is little, at least in 

 the La Grange pool, to vary this monotony of mud banks and 

 fringing willows. The backwaters have been reduced to the 

 lakes, sloughs, bayous, and marshes which abound everywhere 

 in the bottom-lands. Many of these, as, for example, Phelps and 

 Flag lakes, have ceased in their reduced condition to contribute 

 to the river. Others, like Thompson's Lake, maintain a connec- 

 tion with the river by means of a long and tortuous bayou or 

 slough through which the current flows in or out as the relative 

 levels of the two fluctuate. This lake receives but little water 

 from a few springs and creeks along the bluffs, and like many 

 others in the bottom-lands serves only as a reservoir from which 

 the wateri s slowly drawn off as the river falls, but when once 

 the lower stages are reached its contributions cease. Still others, 

 like Quiver and Matanzas, maintain direct and open connection 

 with the river, and since they receive tributary streams they 

 continue to feed the river, but in reduced volume. Though the 

 number of tributary areas is thus much reduced at low-water 

 stages, the individual peculiarities of the tributary waters in the 

 bottom-lands become more pronounced. As each one loses its 

 connection with the general flood it becomes a separate unit of 

 environment, with its local differences in those factors which de- 



