Macroinvertebrates (continued)

According to Tucker’s study, conditions are improved in the central portion of the river, but remain the same in the upper reaches, from Joliet to Lacon. Table 28 contains the stream classifications for areas from Joliet to Grafton. Samples are taken in September and October of 1967 and August and October of 1978. From Joliet to Seneca, 33 miles, the river is semi-polluted; a transition zone of 67 miles from semi-polluted to unbalanced occurs between Marseilles and Chillicothe. From Chillicothe to Havana, 60 miles, the river shows improvement, and downstream of Havana to Grafton conditions fluctuate from unbalanced to balanced.

Table 28: Comparison of Stream Classifications* of the Illinois River, 1967 and 1978 (Tucker)

*Key: Bal = Balanced; UB = Unbalanced; SP = Semi-polluted; Pol = Polluted