. Bulletin. Natural history; Natural history. 354 Illinois Natural History Survey Bulletin Vol. 30, Art. 5 tion equivalent of 386,000 (United States Public Health Service 1963: 111-5). Mr. Edwin Fall (pars, comm., 24 February 1969) informed the author that the estimated population equivalent of treat- ed and untreated domestic and industrial wastes entering the river in 1960 from Peoria was about 100,000, but as in- dicated above, this has been reduced considerably since 1960. The remaining 150 miles of the river from Pekin to Grafton received only agricultural runoflf and effluents from small
. Bulletin. Natural history; Natural history. 354 Illinois Natural History Survey Bulletin Vol. 30, Art. 5 tion equivalent of 386,000 (United States Public Health Service 1963: 111-5). Mr. Edwin Fall (pars, comm., 24 February 1969) informed the author that the estimated population equivalent of treat- ed and untreated domestic and industrial wastes entering the river in 1960 from Peoria was about 100,000, but as in- dicated above, this has been reduced considerably since 1960. The remaining 150 miles of the river from Pekin to Grafton received only agricultural runoflf and effluents from small communities and a few small industries. Kofoid (1903:198-203) reported that in 1897 sewage from Chicago entering the Illinois River through the Illinois and Michigan Canal at La Salle and from the Peoria-Pekin area was one of the most important factors causing an abundance of plankton in the Havana area. Apparently pollution did not be- come detrimental to aquatic life in the La Grange pool until after 1915 (Rich- ardson 1921&:49). Richardson (1925&: 411) limited his collecting to small bot- tom fauna organisms in the La Grange and Alton pools, and as a result, the effects of pollution in the 1915-1920 pe- riod on mussel life in these pools were not recorded. Between the 1913-1915 period and the summer of 1920 the dis- solved oxygen at Havana dropped from 4 ppm to 1 ppm (Richardson 1925a: 327-328). During this period pollution eliminated about 70 kinds of benthic organisms other than mussels from the river near Havana and 24 or more kinds between Havana and Beardstown (Rich- ardson 1925^:410-413) (Fig. 14). In 1917 Richardson (1925a: 329) observed a heavy mortality of snails in various parts of the river between Spring Valley and Havana. Between 1870 and 1912 at least 43 different kinds of mussels were known to have occurred in the mainstream of the La Grange pool (Table A-21), whereas only 18 kinds were collected alive from the mainstream of this pool in 1966 (Table A
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