among fishes from the Upper Illinois than from the middle and lower 

 sections. 



The abundance of certain species in the electrof ishing collections 

 from Starved Rock Pool, in relation to other pools, indicates a localized 

 pollution problem of some sort, perhaps associated with the entry of the 

 Fox River into this pool. Carp, goldfish, and carp x goldfish hybrids 

 were more abundant here than in pools immediately above and below it. 

 All three of these fish can tolerate low oxygen levels. Members of the 

 sunfish family, including largemouth bass, bluegill, and white crappie, 

 require higher oxygen levels, and were generally less abundant in Starved 

 Rock Pool than in pools immediately above and below. Although dissolved 

 oxygen levels in the Fox River are generally close to saturation, the 

 entry of the Fox into the Illinois causes only a fraction of a milligram 

 per liter increase in dissolved oxygen (Butts, et al. , 1975). During 

 low flows, an oxygen sag develops in the next pool upstream from Starved 

 Rock Pool, Marseilles Pool, and continues into Starved Rock Pool, so 

 that Starved Rock Pool has lower oxygen levels during low flows than 

 Marseilles Pool or the upper end of Peoria Pool (Butts, et al . , 1975). 

 Reaeration of river water does not take place at Marseilles dam during 

 low flows, because the entire flow of the river is diverted through a 

 power plant (Butts, et al. , 1975). 



Table 35 summarizes the commercial catch of fish from the Illinois 

 River and for comparison, the catch from the Mississippi River bordering 

 Illinois. In spite of the improvement in the electrof ishing catch in 

 1973 and 1974, apparently due to high-water levels in 1971-1973, the 

 commercial catch of fish in the Illinois River continued its historical 

 decline in the 1970' s. There was a slight increase in the catch in 1974, 

 probably due to fish spawned in 1971-1973, which were of large enough 

 size in 1974 to be taken commercially. Nevertheless, the general trend 

 since 1950 has been downward, and depending on whether the Illinois 

 Department of Conservation or the "Fisheries Statistics of the United 

 States (1950-1971)" are used, the catch dipped under one million pounds 

 for the first time in 1971 or 1972. The decline is not explained by a 

 decline in the number of commercial fishermen — there were 13 full-time 



