with treatment since 1924. Table 40 shows the number of municipal and 

 industrial sources of pollution within the major drainage basins in 

 Illinois in 1927 as taken from Buswell (1927: 9). The data show that there 

 were some 54 sources of municipal and industrial pollution along the 

 Mississippi River from the Wisconsin border to the Illinois River mouth. 

 This compares to 256 combined sources in the Illinois River drainage 

 basin (exclusive of the Metropolitan Sanitary District) . 



In a 1944 survey of the Mississippi River from Hastings, Minnesota 

 (Mississippi River mile 814.0) to Caruthersville, Missouri (110 miles 

 below Ohio River mouth), Platner (1946: 71) reported that 



the sum of all polluting effluents now entering the Missis- 

 sippi River in the sector studies, are not creating condi- 

 tions seriously unfavorable to fish and other aquatic life, 

 except in local areas below particular plants or cities. 



The following discussion of pre- and post-construction water quality 

 parameters is broken down into four categories: (1) dissolved oxygen, 

 (2) turbidity, suspended sediment, and water clarity, (3) nutrients, 

 and (4) heavy metals and pesticides. 



Dissolved Oxygen . In the early days of assessing water quality, 

 investigators felt that the degree of municipal sewage pollution was 

 best indicated by dissolved oxygen concentrations of receiving waters. 

 Therefore, water quality data collected and presented during the pre- 

 construction period were primarily dissolved oxygen levels and/or dis- 

 solved oxygen saturation values. In a comparison of the dissolved oxy- 

 gen values in the Mississippi and Illinois Rivers near Grafton, Illinois 

 (Mississippi River mile 218.5) in 1900, A.W. Palmer (Bartow, 1913: 32) 

 found that the percentage of saturation averaged 76.5 percent (range 2-7 

 mg/1 0„) in the Illinois River, while a parallel series of samples from 

 the Mississippi River averaged 82 percent (range, 3-8 mg/1 0„) . 



In 1926, the U.S. Bureau of Fisheries evaluated the effects of mu- 

 nicipal pollution from the St. Paul-Minneapolis, Minnesota area (Missis- 

 sippi River mile 851.0) on water quality in that reach of the Mississippi 



130 



