134 
BULLETIN OF THE BUREAU OF FISHERIES 
CONCLUSIONS 
It remains to give our speciai observations regarding the fishes of commercia] 
importance possibly affected by the dam and to consider each in the light of all 
available information concerning them. For reasons of practical convenience this 
is made the subject of a special report to follow, entitled “Studies of common fishes 
of the Mississippi River at Keokuk.” (Coker, 1930.) However, it is appropriate 
here to give our conclusions in full, and this is done with the understanding that the 
data supporting many of the conclusions presented are to be found in considerable 
part in the other report. 
The dam acts as an effective barrier to upstream movements of fishes, being 
impassable in that direction for any kind of fish except in so far as they may pass 
through the lock. The evidence indicates that there is no distinct migratory move- 
ment of fish through the lock. The location of the lock with reference to the currents 
and the manner and extent of its operations preclude its functioning as an effective 
fishway. 
Little evidence was found to indicate that free migration past any one given 
point in the river as far north as Keokuk is of vital importance to any species of fish 
of the region except the eel, river herring (“skipjack”), Ohio shad, blue sucker 
(probably), and possibly the rock sturgeon. Each of these fish is mentioned severally 
in the following paragraphs. 
Fish may pass over the dam in a downstream direction, but we could find no 
evidence that this occurred to a detrimental degree for any kind of fish, excluding 
the eel. 
Reports that fish in upstream migration were deflected in quantity up the Des 
Moines River, a tributary entering the Mississippi River just below the dam, were 
carefully investigated on two occasions in different years and were found to be 
manifestly without foundation in fact on these occasions. 
Injured fish, chiefly paddlefish, frequently are seen floating in the swift current 
just below the dam and near the western shore. Many experiments were made, 
but the cause of the injuries could not be determined. It was learned by experiment 
that carp and goujon could pass over the dam without evident injury, and that it 
was possible for paddlefish to pass downward through the turbine chambers without 
observable injury. It does not follow, of course, that fish could not receive injury 
in making such passages. There is the possibility that the injuries resulted from 
encounters with submerged piling in the extremely swift waters of the tailrace. 
Studies of the records of river level for both Davenport (above the lake) and 
Keokuk (below the lake) for the years 1910 to 1919, inclusive, show that the fluctua- 
tions tended to become more marked in the later years at both places. 
While a lake of considerable expanse and depth now covers the site of the former 
Des Moines Rapids and adjacent sections of the river and its bordering lowlands, 
typical lakelike conditions have not developed and probably never will develop to an 
extent comparable to the conditions in Lake Pepin. Both lakes represent impounded 
portions of the river — the one artificially impounded, the other naturally impounded. 
The differences between the two are attributable to the greater volume of the inflow- 
ing river relative to the area of Lake Keokuk, the greater amount of sediment carried 
by the river in its lower course, and the reclamation of a very valuable portion of 
the lower lake for agricultural uses. The increase of plankton in Lake Keokuk 
