436 



Bureau of Fisheries. The factors entering into the increase of the fish 

 yield were principally : 



(1) The introduction of the German carp. 



(2) The increase in fishing operations. 



(3) The increase in the area of the river due to the addition of 

 water from Lake Michig^an. 



(4) The increase in the food supply resulting from the sewage. 



Since 1008 there has been a marked decrease. A census taken by 

 the U. S. Bureau of Fisheries in 1921, a poor fishing year, showed 4 mil- 

 lion pounds ; and in 1922, a favorable year for fishing, the census showed 

 lOJ/2 million pounds. The factors entering into this decrease are: 



(1) The reclamation of the bottomlands and lakes along the middle 

 and lower sections of the river. 



(2) The exclusion of fishes from large areas of the upper and 

 middle river during a large part of the year, due to conditions produced 

 by an excess of sewage. 



(3) Occasional periods of extraordinary pollution which wipe out 

 whole populations of organisms that ser\-e as fish food and which destroy 

 large numbers of the fishes themselves in places where they can not re- 

 treat into better water. 



Messrs. Alvord and Burdick, in their report on "The Illinois River 

 and its Bottomlands" (1915), have shown that the fish yield is closely 

 correlated with the water area. In the Beardstown-Grafton section of 

 the river there has been no very marked change in the amount of fish 



i 



