76 ILLINOIS BIOLOGICAL MONOGRAPHS [174 



that after rains, when the stream rapidly rose, putrescible matter was 

 washed down stream, cast on shore, and the odor was then very bad. This 

 lasted until the water subsided. In the fall of 1920, the same people were 

 again interviewed and conditions were reported to be much worse than 

 previously, the unusually low stage of the water causing the putrescible 

 matter to decay on the exposed sand bars in the river, from which some 

 odor was noticed. 



Stream measurements of the velocity of the current were made by the 

 Water Survey at several points along the Salt Fork. These were made by 

 Habermeyer on October 1, 1917, when the water was low in the stream. 

 All data given in feet. 



Table IX. Mouth of the Boneyard 



Distance from east bank 1 2 3 



Depth of water 0.6 0.7 0.4 



Flow per hour 4608 4500 4320 



Salt Fork, Four Miles below Champaign Sewer Outlet 



Distance from bank 2.9 2.4 1.8 2.2 



Flow per hour 3888 4320 4212 2412 



These measurements indicate a very slow current, from about one half 

 to nearly a mile an hour. At high water the rate of flow is undoubtedly 

 several times as great. Tliis slow rate of flow would cause much of the 

 heavy matter in the sewage to be precipitated to the bottom and form 

 sludge banks, and this has occurred at many places below both the Urbana 

 and Champaign outlets. High water and more rapid current probably 

 moves some of this sludge farther down stream, also carrying the fresh 

 sewage farther down at such times. A recent examination made at very 

 low water indicates that this has been the case, for hundreds of bars were 

 observed out of water, each covered with a sludge formation of greater 

 or less size. 



Analyses of water from various places in the Salt Fork and tributary 

 streams have been made by the Water Survey. The two tables that fol- 

 low, taken from Habermeyer's report, indicate some of the conditions of 

 the upper waters of Salt Fork (Tables X and XI). 



In Table X the low percentage of dissolved oxygen (saturation) in 

 the ditched stream above Lincoln Avenue is noteworthy as compared with 

 the larger amount at Cunningham Avenue. At both localities, however, 

 the water is relatively pure, there being little or no pollution. The sample 

 from a mile and a quarter below the champaign outlet is striking because 

 of the total absence of oxygen. The sudden rise in saturation at four 

 and eight miles is also notable, and indicates that at these points on this 

 date little decomposition was taking place. The sample from Salt Fork 

 near Spoon River shows a marked fall in the amount of dissolved oxygen, 



