Forbes. — Survey of Illinois River 79 



The Des Plaines River comes down from the north prac- 

 tically parallel with the shore of Lake Michigan, and re- 

 ceives the drainage canal from Chicago between Lockport 

 and Joliet. Our observations were directed to ascertain 

 what were the conditions in the drainage canal and in the 

 Des Plaines River at the mouth of that canal, at the mouth of 

 the Des Plaines River after the natural waters of the Des 

 Plaines and those of the drainage canal had mingled; at 

 the mouth of the Kankakee, where we had as near the 

 natural Illinois River water as we can now get ; and then in 

 the stream below the union of these two rivers to form the 

 Illinois itself. 



We found a remarkable contrast between the waters of 

 the Des Plaines River and the drainage canal where the two 

 came together, and not the kind of difference one might 

 expect. The canal water was comparatively clean and clear 

 to the eye, the highly dilute sewage it contained being still 

 too recent to have undergone any very important part of its 

 decomposition. 



The Des Plaines River, on the other hand, was loaded, 

 just above the mouth of the canal, with sewage products 

 in an advanced stage of decomposition, and contained also 

 an immense quantity and considerable variety of the organ 

 isms which live in impure water and cannot continue for 

 any great length of time in water which is not contaminated. 

 These same organisms, of course, characterize the water of 

 the Des Plaines below the mouth of the canal. 



The marked difference between these two waters was 

 accounted for by the fact that the Des Plaines. as it came 

 clown from the north past Chicago, was receiving, undi- 

 luted, the sewage of a number of large suburbs of that city. 

 Its current was slow under the low-water conditions of last 

 summer, the weather was very hot, and the stream was 

 shrunken by drouth. The sewage had consequently, time to 

 reach an advanced stage of decomposition and to develop 

 immense numbers of septic organisms before it reached the 

 mouth of the canal; whereas, in the water of the canal 



