142 
INCREASED ACREAGE OF THOMPSON LAKE CORRESPONDING 
to INCREASING LEVELS 
Area of lake increases, for each 
As levels increase from— tenth of a foat, by—= 
4.41 to 5.13 feet 4.72 acres 
5135 tor 16,08!" 8.68> 
6.08 to 7.08 “ LH F4AS 
7.08 to 8.08 ” 4.56 “ 
8.08 to 9.08 “ Boe ee 
9.08 to 10.08 “ 2.56 
10 1396+ 
-08 to 11.08 “ 
3. A secondary effect has been to narrow permanently the belt of 
shallow weedy water along the banks of the stream in midsummer, and to 
do the same, at least temporarily, along parts of the shore of many of the 
lakes. The river waters now commonly reach in midsummer to the bases 
of the willows, permanently covering new banks of steeper slope than the 
original margins, which latter have now generally become too deeply sub- 
merged and too much shaded for rooting water-plants. Some of the 
lakes have lost large areas of rooted vegetation in the deeper parts, per- 
manently, as it appears, while many others whose characteristic vegeta- 
tion was killed out by the deeper water after the opening of the drainage 
canal, are now filling up again with the typical plants of deeper standing- 
water. This destruction of inshore and alongshore vegetation has been 
especially conspicuous in the broad belt of deadened trees and shrubs 
along the banks, especially in the middle course of the stream from Peoria 
southward. Other important effects are beginning to appear as these 
dead trees weaken and fall into the water of the stagnant lakes, fouling 
them, in the hottest weather, with the products of vegetable decay. 
4. The greater depth of the present river, and especially the greater 
depth at low-water stages, must have an effect to diminish ranges of 
temperature, especially in the upper shallower part of the stream. The 
water there can not heat up as rapidly as formerly when exposed 
to the midsummer sun, or reach so high a temperature—a fact which 
must retard decomposition processes now as compared with the period 
before 1900, and thus delay the transformation of sewage materials into 
forms fit for use as food for the normal plants and animals of an unpol- 
luted stream. 
5. Along with the greater average volume of the stream goes neces- 
sarily an increased average rate of flow and a shortening of the time of 
passage of water from point to point and from the source to the mouth. 
This difference is greatest for the lowest stages of water and least for 
the highest, but our computations show that, at usual midsummer levels, 
only about half the time is needed for water to flow the length of the 
stream that was taken before the opening of the canal, about thirteen 
