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BULLETIN OF THE BUREAU OF FISHERIES 
One other feature of the lock must be considered in connection with the possible 
function of the lock as a fishway, and that is its location about one-half mile down- 
stream from the dam proper, close to the Iowa shore and out of the main currents 
from the spillways and from the power house. Such a location, of course, is highly 
favorable to its use for purposes of navigation. 
It is an obvious conclusion that fish engaged in an active upstream migration are 
guided by the direction of flow of the strong current. At Keokuk this would lead 
them past the lock and up toward the base of the dam from a region of generally 
slack water. There is nothing about the lock itself, with its large pool of still water, 
and the entrance to the lock apart from the main current to “suggest to the fish” 
that this is the best avenue of passage to the upper reaches of the river. It is not 
surprising that a large proportion of fishes taken in the lock are such as we associate 
with still waters or as are taken in shore nets — carp, drum, buffalo fishes, etc. 
In regard to the lock, then, the evidence indicates that it does not function as 
an effective fishway. It is located apart from the main streams, and no current 
passes through it. Although it is frequented by a variety of species and many fish 
are stranded upon the upper gate when raised, the observation and experiments fail 
to reveal any evidence of a practical migration of fish through it. Systematic trials 
with a net closing the upper opening of the lock show that there is no considerable 
movement of fish there. The upper gate of the lock takes a few common fish because 
it operates like a dip net — with a very large surface but low sides. The number of 
fish caught thereon is what might be expected of such a device and is not indicative 
of any appreciable migratory movement, although it is possible that migratory 
movements of species are faintly reflected in the catch. Even if its location and 
structure were more favorable to its functioning as a passageway for fish, it could not 
do so effectively, because it is open above only for brief periods of a few minutes at a 
time, and the sum of all its open periods during the spring and early summer (when 
upstream migrations are expected) amounts to scarcely more than a single day. 
CONCLUSIONS REGARDING THE DAM AS A BARRIER 
We have seen that the dam must serve as a practically effective barrier to the 
upstream movements of fish. They can not pass up the spillways or even buffet the 
current below an open spillway. Undoubtedly they can not pass up through the 
turbine chambers. The lock, the only remaining means of passage, does not witness 
any distinct migratory movements through it. It is possible for fish to pass down- 
ward, perhaps through various passages, but especially over the spillways. We have 
no observations to indicate that any considerable number of fish pass from upper to 
lower river over the dam, and it is reasonable at least to suspect that fish engaged in 
a downstream movement would find in the large lake above the dam, with its deep and 
relatively still waters, the conditions ordinarily sought farther downstream, or that 
the slacking of the current in the lake would inhibit a further downstream migration. 
T his would not of course, be the case if there were distinctly anadromous fishes 
(other than the Ohio shad — see Coker, 1930) in the Mississippi — that is, those that 
live in the sea or ascend rivers to spawn — or if certain species must avoid the cold 
waters of a northern climate. 
The actual effect of the dam upon the several common species, as far as our data 
reveal it, will be treated in another place; but it remains in this connection to inquire 
into the general significance of the barrier in the light of observations of migrations 
of fishes at Keokuk. 
