KEOKUK DAM 
113 
The waters at Keokuk can not accurately be called turbulent. They are not hurled over 
hidden boulders and irregular rocks with the speed of a Niagara. The river has much the same 
velocity and presents the smooth appearance of water running down an inclined surface. 
While under such conditions the bottom might be expected to be swept fairly 
clean, there were enough loose rocks and gravel to support very abundant fresh- 
water mussels. No doubt under lake conditions there must occur a gradual accum- 
ulation of silt over the former bottom of the rapids. (See remarks on silting 
in section entitled “Fresh-water mussels” in Coker, 1930. 
ICE 
One striking change has occurred in river conditions. For a distance below the 
plant the river no longer freezes over, because the obstruction breaks up the ice. 
Sheet ice forms in the coves, and a couple of miles south it extends from the banks 
well out into the river. At Warsaw (5 miles south of the dam), in 1915, the frozen 
area extended nearly to the channel from each shore; but, according to information 
supplied by the fishermen, the river was not entirely frozen for another mile down. 
The next year the river probably did not freeze over anywhere south of Keokuk, 
although some informants asserted that it froze entirely across for a short distance 
somewhere between Canton, Mo., and Warsaw, 111. Local informants report con- 
ditions in 1916-17 that were similar to those of 1914-15. Prior to the construction 
of the dam the river usually froze sufficiently so that teams could be driven across 
along the whole region from Canton northward and for some distance southward. 
The open condition of the river has been a boon to fishermen, facilitating opera- 
tions in the winter. Men who used fyke nets reported that anchor ice formed on 
their nets and hampered them. The formation of such ice at the bottom of a river, 
where the current is rapid and the surface open, is a phenomenon that has long been 
known but is not very well understood. (Barnes, 1906, Ch. VII.) 
OXYGEN CONTENT 
No observations have been made on the extent to which the water is oxygenated 
by the Keokuk Dam, but this must be great. The early conditions in the lake 
above, with decaying vegetation, active animal life, and deficient plant life, may 
have caused diminution in the percentage of oxygen below the average for the river. 
So far as the lower river is concerned, this loss probably is fully compensated for 
by the dam. On the Illinois River, Forbes and Richardson (1913, pp. 542 and 549) 
found that polluted water had its dissolved oxygen substantially restored and its 
carbon dioxid diminished by falling over a 10-foot dam. The authors added that 
the difference in oxygen doubtless had its effect upon the abundance of fishes, but 
that the fish population below the dam was small as far as indicated by limited 
observations. The present conditions on the lake are likely to be followed by others 
that will tend to give a higher percentage of oxygen to the water. Since the con- 
ditions have not been investigated, they can be referred to here only as suggestive 
of a significant factor in the influence of the dam upon fish life in the river. 
FLUCTUATION OF RIVER STAGE 
To determine as nearly as possible the effect of the dam in respect to increased 
or lessened stability of river stage below Keokuk, the reports of the United States 
Weather Bureau (Frankenfield, 1911, p. 235; Henry, 1913, p. 219; Henry, 1915, p. 
231; Henry, 1916, p. 89) and later reports have been examined, and, from the daily 
stages given therein, certain computations have been made, and these are embodied 
