22 ILLINOIS ACADEMY OF SCIENCE 



Only a few of the more significant results of this river 

 survey can be mentioned here. Daily observations on the 

 breeding habits of Illinois fishes, and parallel aquarium 

 studies, have given us a considerable body of new informa- 

 tion of importance to fish culture and to the maintenance and 

 improvement of our fisheries. Two papers are in press. 

 Comparisons of the yield of plankton at Havana, on the middle 

 Illinois, for three years preceding, and a year following the 

 opening of the Chicago Drainage Canal, show a greatly in- 

 creased average yield per cubic meter in the river itself and 

 in certain classes of lakes, and an enormous increase in the 

 total product of these waters, to be connected with their in- 

 creased volume and the greater average area consequently 

 covered by them. We find the Illinois at Havana about two 

 and a half feet higher than before the opening of the canal, 

 the plankton yield of the stream itself approximately twice as 

 great to the unit of volume, that of Quiver Lake about three 

 times as great, and that of Thompson's Lake practically un- 

 changed. The plankton product of the river reaches its mini- 

 mum, for the warmer part of the year, when continuous low 

 water isolates its bottom land lakes for a long time, these be- 

 ing reservoirs from which the plankton of the stream is con- 

 tinuously replenished. 



The efifects of sewage contamination upon the system of 

 river life become extreme during long-continued hot weather 

 coinciding with unusually low river levels. Under such condi- 

 tions as prevailed in July and August, 1911, the upper twenty- 

 six miles of the Illinois, (from the mouh of the Kankakee to 

 the dam at Marseilles,) becomes virtually a septic tank, with 

 oxygen ratios averaging one third or less of saturation, at i- 

 time when the waters of the Kankakee just above, are super- 

 saturated ; with carbon dioxide as high as 11 parts per mil- 

 lion, while in the Kankakee it ranged from 2 parts down to 

 zero; and with the gases of the bottom sediments indistin- 

 guishable in composition and proportions from those of the 

 sludge of a septic tank. Fishes were altogether absent from 

 this part of the stream at this time, and the main content of 

 our collections consisted of foul-water organisms mingled 

 with the more resistant species coming in from Lake Michi- 

 gan and from the Kankakee — the latter rapidly diminishing in 

 numbers, however, as they were carried down stream. The 

 only fish mortality noticed which was due to sewage was in 

 the Sanitary canal itself, and in the highly contaminated Des 

 Plaines. Fishes simply withdrew from the more polluted 

 waters of the Illinois into normal or less contaminated tribu- 

 taries. A considerable overturn, both chemical and biological, 

 was made by a 12 to 14-foot fall of the stream over the Mar- 



