I 



course, be much greater; as high as 2,000 lurbidity units 

 have been noted by the Illinois Sanitary Water Board 

 in the lower river during flood conditions. 



Turbidity in parts of Peoria Lake is sometimes in- 

 creased by large populations of minute floating plants 

 known as phytoplankton, but in general the river's lack 

 of clarity is due to suspended silt. Turbidity probably 

 affects the procurement of food by sight-feeding fish 

 (Starrett & Fritz 1965). It also affects production of 

 plankton, and the well-being of various larger forms 

 of aquatic plant and animal life (Ellis 1936). 



DISSOLVED OXYGEN 



Oxygen dissolves in water according to certain phys- 

 ical laws, and ac]uatic life has evolved to live and respire 

 within the normal limits of this solution. Suffocation 

 can take place if waters carry pollutants which will 

 oxidize and remove this gas faster than it can be 

 replaced. This makes too great a demand on the avail- 

 able oxygen, and fish, as well as other forms of ac]uatic 

 life, will die. 



The requirements for oxygen on the part of different 

 aquatic species arc not the same. Trout, for example, 

 require more dissolved oxygen than do carp or goldfish. 

 It appears from Ellis's stu'dies (1937:372-37.3) that 5 

 parts per million (ppm) of dissolved oxygen is the lower 

 limit for maintaining a desirable fish fauna in a river. 

 Tarzwell (1958:19) believed that ". . . for a well- 

 rounded warm water fish population, dissolved oxygen 

 concentrations must not be below 5 p. p.m. for more 

 than 8 hours of any 24-hour period and at no time 

 should they be below 3 p. p.m." Diu'ing the winter 

 months on the Illinois River, Thompson (1925:431) 

 noted that carp and buffalo were found in water having 

 as little as 2.5 ppm of oxygen, but a variety of fish was 

 found where there were 4 ppm, or more, and the greatest 

 variety was found where there were 9 ppm. We also 

 have foimd fish living in water with below 3 ppm of 

 oxygen ; however, we believe that prolonged low oxygen 

 conditions are having a drastic effect on acjuatic orga- 

 nisms in the river. 



Continuous low oxygen determinations indicate that 

 pollutants carried by the stream have a high biological 

 and chemical demand on the oxygen supply and that the 

 stream is in poor condition for fish life. Because the 

 quantity of dissolved oxygen in tlie Illinois River water 

 becomes an important limiting factor and has a strong 

 relationship to the health of the organisms living in that 

 water, it is important that we briefly review this factor. 

 That low dissolved oxygen is a present as well as a 

 past problem is indicated bv the readings presented in 

 Table 1. 



Prior to 1800 the entire Illinois River syslcTu wilhoul 

 doubt carried enough oxygen to support a well-diversi- 

 fied, healthy, fish population. Possibly a turning point 

 occurred when the flow of the Illinois and Midiigan 

 Canal was reversed and began to biing sewage from 



Chicago to a point in the river at La Salle in 1871. The 

 Peoria-Pekin area also began to develop along the 

 middle stretch of the river. Sewage and industrial wastes 

 coming into the river were untreated. 



Kofoid (1903:199) estimated that the Illinois River 

 received the untreated waste from a population of 

 1,032.229 people in 1890. There were no statistics as 

 to the gallonage that this represented, but considering 

 the pumpage into the water systems of the cities as an 

 approximation of the sewage flow, he calculated that in 

 1897 the flow was 540.529,061 gallons per day. Kofoid 

 stated (loc. cit.:230) that before the Sanitary and Ship 

 Canal was opened in 1900 the nitrogenous material in 

 the Chicago sewage was in the process of rapid oxidation 

 in the upper reaches of the Illinois and Michigan Canal 

 near Lockport, and that the process was largely com- 

 pleted by the time the canal water reached the Illinois 

 River. He also said that in the summer months the 

 wastes from Peoria were well decayed before reaching 

 Havana, although in the winter the sewage was not so 

 well oxidized. 



As mentioned earlier, the opening of the Sanitarv 

 and Ship Canal in 1900 brought into the Illinois great 

 quantities of sewage-laden lake water. Forbes & Richard- 

 son (1919:139) mentioned that in 1913 the flow of the 

 Sanitai-y and Ship Canal amounted to 85.7 percent of 

 the flow of the original river at Peoria. 



By 1911 the upper part of the river was heavilv 

 polluted. Forbes (1911:5-6) stated: "Immediately 

 below the mouth of the canal we have in the Des Plaines 

 a mingling of these waters, and the Illinois River itself, 

 below the jimction of the Des Plaines and the Kankakee, 

 the septic contributions of the former stream are largelv 

 diluted by the comparatively clean waters of the latter. 

 Nevertheless, we had in July and .■\ugust what mav be 

 called se]3tic conditions for twenty-si.x miles of the course 

 of the Illinois from its origin to the Marseilles dam. At 

 Morris, which is on the middle part of this section, the 

 water, July 15, was grayish and sloppy, with foul, pri\y 

 odors distinguishable in hot weather. . . . Putrescent 

 masses of soft, grayish or blackish, slimy matter, loosely 

 held together by threads of fungi and densely covered 

 with bell animalcules, were floating down the stream ; 

 and chunks of this material, from the size of a walnut 

 to that of a milk pan, occasionally rose to the surface, 

 c\idently borne up by the gasses developing beneatii 

 them." He found that at that time the dissolved oxygen 

 at Morris was only 9.8 percent of satination. Sixteen 

 miles below Morris, at Marseilles, the oxygen was onlv 

 7.5 percent of saturation. However, in the unpolluted 

 Kankakee River 9 miles above Morris the dissolved 

 oxygen was 1 12 percent of satination. 



The oxygen determinations gi\en in Table 1 show 

 how polluted the Illinois River was in 1911 and 1912 

 from Morris to Peoria. 



Clonditions became men worse during and imme- 

 dintelv following World W.n 1. Purdy (1930:2), who 



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