338 



Upper Peoria Lake and the Illinois River, Chillicothe to 



Spring Bay. (Mile 146.5—153.2 below Lake 



Michigan) 



Hydrography 



The three cross-sections in the upper lake district in 1022 began 

 with one in the river proper at Chillicothe. which is only a half mile 

 above the present low-water head of the upper lake, 6.7 miles above 

 its approximate foot at Spring Bay, and 14.5 miles above the head of 

 the lower lake at Peoria Narrows. The two cross-sections through 

 the lake proper included one at Rome, 2.8 miles below Chillicothe, 

 where the extreme width at recent summer low water has been in the 

 neighborhood of 4,800 feet; and one on a line a mile and a half above 

 Spring Bay, 5.2 miles below Chillicothe, where low water widths have 

 recently been somewhat more than G.OOO feet. ^lid-channel depths 

 at Chillicothe in August 1922 were around 22 feet, but were only 13 

 or 14 feet opposite Rome and Spring Bay, at the first of which places 

 considerable filling has evidently occurred since 1901. The soiuidings 

 made in the east wide-waters opposite Rome were not over 6.5 feet 

 in the first 1,500 feet; and did not exceed 5 feet in the next 2.000. A 

 mile and a half above Spring Bay depths in the open lake were nnich 

 greater, nine- fo more than ten-foot soundings continuing for 3.500 

 feet beyond the mid-channel line on the east or widest side. The 

 bottom in the river at Chillicothe was deep mud ; and throughout the 

 upper lake was uniformly soft black nuid at the stations visited, except 

 on the far west side above Spring Bay, where harder mixed nuid and 

 gravel bottom reaches out a hundred feet or more from the bank at 

 low water. 



Though the odors of the bottom sediments in the upper lake 

 showed striking differences between 1915 and 1920, as described in a 

 previous paper, it was not always an easy matter to make out reciUy 

 definite differences between the summers of 1920 and 1922. While 

 some average improvement evidently occurred in the two years, it 

 wa^ clear also that there was still abundant room for more. Sum- 

 marizing the records from this portion of the lake for the summer 

 of 1922, it is fountl that we noted abundant bubbling at all stations; 

 distinctly foul odors at seven stations out of the total of twenty-three ; 

 mildly bad odors at nine out of the twenty-three stations ; and had no 



