ILLINOIS AUDUBON BULLETIN 3 
Tue Errects Or CHANNELIZATION 
ON 
Fiso POPULATIONS 
by MIKE CONLIN 
Division of Fisheries 
Illinois Department of Conservation 
Channelization is the conversion of a natural meandering stream or 
river to a ditch for the purpose of moving water rapidly downstream. This 
sluicing of surplus rainfall off the land speeds the rush of floodwaters from a 
given area. Yet, this practice frequently compounds the flood damage in 
downstream sections. 
Often labeled as channel improvement or stream restoration, chan- 
nelization typically requires clearing of a swath 100 feet wide along each 
bank to provide working space for heavy equipment. The materials removed 
from the sides and bottom of the stream are deposited as spoil along the 
banks previously occupied by trees, shrubs, flowers and wildlife. After 
widening and lowering of the natural channel, denuded banks are usually 
sloped and sometimes rip-rapped with stone or concrete. 
The clearing of streamside vegetation often results in significant rise in 
water temperature which adversely affects the life histories of many species 
of fish and lower aquatic organisms. Increased temperature may prompt 
impaired respiration, slower growth, lowered resistance to disease and 
pollutants, and may interrupt the spawning cycle. The loss of streamside 
vegetation reduces the number and types of terrestrial insects available to 
fish populations. Insects falling from bank vegetation serve as an important 
dietary component, especially during late spring and summer. 
Water turbidity and stream siltation increase markedly following the 
removal of bank cover. Increased turbidity diminishes the transmission of 
light, which reduces or may even eliminate the production of plants. Algae 
