539 



It should be said, with respect to the present scarcity of several 

 of these species as compared with previous times, that the causes 

 are probably complex, and are not to be sought in differences of 

 the water only. As has been shown in another place*, a great stimu- 

 lus to fishing operations, due to an enormous multiplication of Euro- 

 pean carp, may well have had the effect to reduce the numbers of 

 many native species whose haunts and habits are such that they are 

 likely to be caught by the same apparatus and operations as the carp. 



A comparison of this account of Chillicothe conditions and col- 

 lections with those for Morris and for Marseilles above the dam will 

 show the main features of the effects of a sewage polhition of the 

 river and the completeness of the biological, if not the chemical, 

 recovery within ninety miles below. 



Summary by Stations 



The Sanitary Canal at Lockport. — Although the water of the 

 canal at Lockport was comparatively clear, with an inoft'ensive odor 

 even in August and September, 191 1, it was not only rather heavily 

 loaded with putrescible materials from Chicago sewage, mainly as 

 yet undecomposed, but it was lower in oxygen content at most times 

 than the river water either of the Des Plaines or the Illinois at any 

 point where our tests and collections were made. In the winter 

 however, the amount of oxygen in solution approximated the ratios 

 of an unpolluted stream, being actually higher in February, 1912, 

 than at any point between Lockport and Peoria. This is to be un- 

 derstood, of course, as due to the gradual start and slow develop- 

 ment of the self-purification process in cold weather. Many small 

 fishes came down the canal in summer and fall, mostly dead when 

 they reached Lockport, although many "shiners" were still alive, but 

 in a dying state. There were no living snails, crustaceans, or water- 

 breathing insects in the water or on the bottom, and except for a 

 few green algre and other minute organisms on the riprap at the 

 edges, the plants and animals were those of a polluted stream. These 

 were, however, very much less abundant here in summer than in the 

 Des Plaines beside the canal, or in the main river below. 



The Des Plaines River at Lockport. — The condition and contents 

 of the D'es Plaines at Lockport, where the stream runs beside the 

 sanitary canal, vary greatly with varying circumstances — local, sea- 

 sonal, or merely meteorological. In the summer of 191 1, the whole 



*"The Native Animal Resources of the State." Stephen A. Forbes. Trans. 

 Fifth Ann. Meeting, 111. State Acad. Sci., pp. 4^-43- 



