437 



taken. Here the factors making for increased yield have been offset 

 largely by reclamation of the bottomlands. The greatest change took 

 place in the Peoria-Browning section, where there was a marked increase 

 in fish yield up to 190S and an equally marked decrease after 1908. Here 

 the reclamation of bottomlands, notably the Thompson's Lake district, 

 took place several years later than in the lower section of the river. In 

 the upper section (La Salle-Chillicothe), although considerably less land 

 has been reclaimed, and the higher stage of the river has increased the 

 area of water, the fish yield shown by the 1921 and 1922 figures is scarce- 

 ly half its former value. This decrease has been brought about entirely 

 by the conditions produced by an excess of sewage.. The most important 

 effect of an excess of sewage is the reduction of dissolved oxygen to a 

 point where fish life is excluded from immense areas of water. 



