I 



MAN'S EFFECT ON THE FISH AND WILDLIFE 

 OF THE ILLINOIS RIVER 



Harlow B. Mills, William C. Sfarrett, and Frank C. Bellrose 



THIS IS A DOCUMENTED REPORT on changes 

 in the Illinois Ri\er, primarily in the past 75 years, 

 with emphasis on the biological modifications which have 

 occurred and are occurring as a result of man's activities. 



The Illinois Ri\er has been called the "most studied"' 

 ri\er in the world. Certainly there is a great heritage of 

 biological information obtained from this stream. We 

 have drawn freely on the observations of Kofoid, Forbes, 

 Richardson, and many others, and have included more 

 modern observations which we and some others have 

 been in a position to make. 



The river has not shown steady changes from year to 

 year. Rather, many of them have occurred with great 

 rapidity and some have not been permanent. For ex- 

 ample, the acreage of water, which went up greatly due 

 ic) di\ersion from Lake Michigan in 1900, was reduced 

 almost to its pre- 1900 surface by 1913. This reduction 

 was due to the development of levee districts, which 

 claimed and drained large areas of the floodplain, and 

 subsequently to decreased lake water diversion in the 

 19.30's. 



Most of the observations in this publication relate lo 

 the main stream and its lateral bottomland lakes, t)ul 

 these areas are only what the basin makes them. 



THE RIVER AND ITS BASIN 



Till' basin of the Illinois River and its ti ibutarii'S is 

 comprised of 32,081 scpiare miles, which is more than 

 half the area of the state of Illinois (Bariows 1910: 1). 

 The name "Illinois" is applied to that part of the chain- 

 age below the confluence of the Kankakee and Dcs 

 Plaines rivers southwest of Chicago, the Kankakee 

 rising in Indiana and the Des Plaines in Wisconsin. The 

 group of glacial lakes in the northeast part of the state 

 drains into the Illinois River through the Fox Ri\cr. 

 The Illinois River is 272.4 miles long, and ilii- cniirc 

 waterway from Lake Michigan lo the mouth of ihc 

 river is 327 miles long. 1 he livcr flows nearly west lo 

 Hennepin where it turns abiuplly southwest, arriving 

 at the Mississippi near Grafton, above St. Louis (Fig. 1 ). 

 Thus, it traverses a large section of l\ni slate, and is 

 affected by and affects the majority of the stale's citizens. 



Barrows (op. cit.) referred to the Illinois valley as 

 the most conspicuous topographic feature of Illinois. Ilr 

 stated that, ". . . certain peculiarities of ihc lower Illinois 



This j)apc'r is puhlishrct by aulhorily i>f the Stale of IltiiiiiiH. IR.S CM, 

 127, Far. .iH.Ili. It is a ( ntitriliutioii frtiiii tlie SectioiiN of A(|ii.'itir ftinltii^y 

 and Wildlife Kpsrarrli of the Illinois .Natural History .Survey. Dr. Harlow 

 B_. Mills is Clhief of the Survey. Dr. William C. Starrell i.s an At|iia(ir 

 Biologist, and Frank C. Bellrose is a Wildlife Spcrialist. 



render it unic|ue among rivers, the region is one of par- 

 ticular interest. . . . The lower Illinois presents a second 

 peculiarity in its remarkably gentle fall. . . . The average 

 fall between Hennepin and Pekin, a distance of .5.'). 8 

 miles, is 0.82 inch per mile. The Illinois is a river of 

 relatively insignificant volume. Its natural low-water dis- 

 charge is less than that of the Rock River and but a 

 small fraction of that of the upper Mississippi and Ohio 

 rivers. The nearly level channel and the small volume 

 result in a very sluggish river, which has bei'n described 

 as a stream that 'more nearly resembles the Great Lakes 

 than an ordinary river,' and again as one that 'partakes 

 more of the nature of an estuary than of a river.' It is 

 wholly unecjual to the task of washing forward the sedi- 

 ment delivered by its headwaters and its numerous 

 tributaries. . . . The average fall of the lower Illinois is 

 less tlian that of the Mississippi below the mouth of the 

 Illinois. This is tin- reverse of the normal relation be- 

 tween tributaries and their main streams." 



This unique condition for a river has been brought 

 about by the present stream flowing through much of 

 its lenglh in a valley developed in the late Pleistocene 

 epoch. During that lime a much larger water volume 

 produced by receding glacicis fashionetl llie present 

 physiogiaphy. 



It might be well lu-ic lo describe the Illinois Ri\fr's 

 bottomland lakes (lateral levee lakes). The river, flow- 

 ing in its uimsually wide valley and carrying a silt load, 

 drops more of this silt at the quieter edges than in the 

 more rapid stream center. This builds u]3 low natural 

 levees along ils shores. Overflow of ihe river at high 

 water leaves large impoundments behind these levees 

 as the water recedes. Usually these impoundments are 

 shallowly connected with the river al iheir upper anil 

 lower ends. 



Man's trealnienl of the i i\cr has tended lo aggravate 

 ils natural tendency to deposit sediment. The building 

 of several dams across the river for navigation purposes 

 iias lendfd lo slow the water even more. Also, the greater 

 tillage (if the agi icultural ujjland has increased the 

 amount of sill that is carried into the quiet mainstream 

 waters. 



The Illinois River was the highway for exploreis of 

 the area, and early settlements were made on its shores. 

 Many early writers were impressed by it. 



Following an ascent of the Illinois River in 1673, 

 Marquette (Kenton 192.5) wrote as follows: "We lia\e 

 seen nothing like this river that we enter, as regards to 

 its fertility of soil, its prairies and woods; ils cattle, elk, 

 deer, wildcats, bustards, swans, ducks, parroquets, and 



