KEOKUK DAM 
115 
then, either climatic or other conditions in that part of the Mississippi Basin above 
Davenport have caused greater fluctuations of river stage in years subsequent to the 
construction of the dam than in years immediately preceding. The facts coincide 
with the suggestion made on page 88, above, that under modern conditions fluctua- 
tions of river level are tending to become sharper and more extreme. There seems 
to be further support for that suggestion in information communicated to the author 
by the Mississippi River Commission in a letter of April 4, 1927, referring primarily 
to another matter : 
The records of this office cover only 15 low waters at Keokuk, 10 of which were below zero. 
The lowest was 2.8 feet below zero (481. SO feet above Memphis datum) on December 18, 1922. 
The creation of a constantly higher level for some miles northward of Keokuk 
may have reduced the capacity of this portion of the river to take up floods; in other 
words, the floods become largely concentrated at Keokuk. Conversely, it is neces- 
sary, when the river is falling, to hold back water to maintain the constant level of 
the lake, and this, of course, occasions a more rapid fall below. Earnest efforts, it 
is believed, are being made by the company to maintain as stable conditions as 
possible below, and their records showed improvement in 1916. These efforts are 
made with the object of avoiding the infliction of damage to steamboats, but the 
results are of advantage to the fishery, for violent and excessive changes would result 
in the stranding of fishes, as actually occurred at the beginning through inexperience. 
(Coker, 1914, p. 10.) 
LAKE KEOKUK 
CREATION OF A RIVER LAKE 
The Keokuk Dam has changed the Des Moines Rapids and a part of the river 
above them info a large area of relatively still water. (Figs. 2 and 17.) From the 
biological as well as from some other standpoints this is a matter of great interest. 
For this body of water the name Lake Cooper was commonly used and will be found 
in the literature, but the United States Geographic Board (1916) has decided upon 
the name “Keokuk Lake.” 
Stockard (1907, p. 758) remarks upon waters of this intermediate character as 
follows : 
Other such lakes still retain a direct connection with the river and are termed by the fishermen 
“river lakes.’’ In these there is a current, which often becomes very strong during the spring 
freshets, when the water of the Mississippi River rises. 
The present author (Coker, 1914, p. 9, footnote) defined the term as meaning 
“such a body of relatively still water as would ordinarily be called a lake, which is 
yet intimately connected with a river, either as interpolated in the course of the river 
or as an arm of a river.” 
It is scarcely necessary to add that there exist waters intermediate between 
river-lakes and rivers, on the one hand, and between river-lakes and lakes on the 
other. The distinction is one of degree but none the less valuable for that reason. 
The biological conditions of the lake in 1914 were studied by A. A. Doolittle, 
and a summary of his observations is presented in another section of this report 
(p. 118). A more exhaustive and continued investigation of the lake would have 
been of great practical importance, but, unfortunately, it could not be arranged to 
continue or to report upon the survey until the observations of Doctor Galtsoff 
were made in 1921 (p. 119). It is necessary for our present purpose, before discussing 
