373 
of the shallower lakes, and the poorest those sections of the river channel 
which are swept comparatively bare of sediments by a relatively swift 
flow. In the river itself much the most abundant product is found where 
the current is most sluggish, and the bottom sediments are consequently 
deepest and are most heavily charged with organic materials originallv 
washed into the stream by rains or poured into it by sewers of cities and 
towns and transformed by oxidation into compounds suitable for the 
nutrition of clean-water plants and animals. 
In a stretch of the river above Havana, which, with its adjacent 
lakes, is the richest part of the Illinois River system, the inshore and 
bottom fauna of the lakes averages in weight to the acre about twice as 
much as that of the river, and it is in the lakes that the fisheries give their 
highest yield. The bottom soils of the lakes are, indeed, richer in or- 
ganic matter, as a rule, than are those of the river opposite, and the muds 
of the marginal waters of these lakes are richer than those of their deeper 
parts—facts traceable, in part, no doubt, to the more abundant light and 
higher temperature of the shallower waters and the consequent greater 
growth of plants whose decay enriches the soil from which they sprang. 
At ordinary high-water levels the current of the river from Chilli- 
cothe to the mouth varies from one to two miles per hour according to 
the slope of the bottom, the width of the bed, and the presence or absence 
of obstructions; and at the highest water it does not much exceed three 
miles per hour for any important distance. At ordinary midsummer levels 
the current rate per hour varies in different sections from half a mile to 
a mile. At lowest water it drops, between Chillicothe and the foot of 
Peoria Lake, to as little as .29 mile per hour. 
Above Havana the bottom, both along the shores and in the channel, 
is, with some exceptions, a rather deep black mud, but below Havana 
this shades gradually into hard clay or sand and shells, soft mud failing 
completely in the channel for long distances. The quantity of inshore 
vegetation is negligible in the river proper, even in the driest seasons, 
since the opening of the sanitary canal of the Sanitary District of Chicago 
in 1900. The bottom-land lakes between Copperas Creek and Lagrange 
are gradually filling with river silt and a growth of plants. A few have 
sandy beaches next the eastern bluffs, but the bottoms of all are otherwise 
of deep black mud, mixed in the shallow water along shore with coarse 
rotting vegetation. In midsummer the margins of all the deeper lakes, 
to a depth of four to six feet, are well supplied with vegetation, while the 
shallower lakes are in many cases weedy over their entire acreage. 
From Chillicothe to Lagrange the animal life of both channel and 
shore waters is almost wholly mollusks (86 to 99 per cent. in collections 
made), but below Lagrange insect larvae (caddis-worms and May-fly 
larvae) were more abundant than above in the shore muds, the ratio of 
mollusks falling to 31 to 65 per cent. In the deeper, opener lakes, mol- 
lusks made 77 to 96 per cent. of the collections, and in the shallower, more 
weedy lakes, 36 to 79 per cent. 
