94 
BULLETIN OF THE BUREAU OF FISHERIES 
far as it was possible to do so, and as they skirted the main streams from the spill- 
ways they would be led in many cases to the base of the dam. In the second 
place, the aeration of the water would be highest just below the falls, and this condition 
might be attractive to fish, particularly just before the season of reproduction. 
Finally, it is not unlikely that a good deal of food is brought over the dam from the 
pool above, which would serve as bait to draw the fish as near as possible to the 
dam. Whatever the cause, it seems to be a common observation that fish are found 
abundantly below dams at certain seasons and particularly in the first years after the 
construction of a dam. The investigators have, therefore, kept a careful watch for 
aggregations of fish, of any species at or near the base of the dam. Conspicuous 
aggregations of fish, however, have rarely been observed at Keokuk, occurring much 
less frequently than was expected and apparently with no regularity. 
While our visits were only occasional during 1913, 1914, and 1917, it must be 
kept in mind that an observer was in regular attendance during two complete open 
seasons — 1915 and 1916. The first recorded aggregation of fish was reported by 
Thaddeus Surber in 1913, only a few weeks after the dam was closed. (Coker, 1914, 
p. 10.) Fish were seen first below the dam on July 10 and 11 in such numbers that 
local residents captured them not only with hook and line but with dip nets and hay- 
forks. The fish seemed to have been found in the following order of abundance: 
Buffalo, carp, paddlefish, sheepshead, drum, channel catfish, redhorse, Missouri or 
blue sucker, toothed herring, and hickory shad. It may be remarked that many of 
these fish are not particularly migratory. 
The next conspicuous aggregation of fish was observed by the writer in the 
following year on April 29, when only one species, the river herring, was in evidence. 
The distribution of the herring on this occasion has been described in the following 
words (Coker, 1914, p. 25): 
The day of my arrival, April 29, was cold, windy, and cloudy, and at first view very few herring 
were observable. After closer observation, however, they were seen to be present in immense 
numbers, and congregated in certain locations * * *. A large number were seen just below 
the short section of dam between the upper end of the lock and the lower end of the power house; 
many were observed along the outer wall of the tailrace, but in the angle between the power house 
and the dam and from this point to the nearest open spillway, a short distance away, the herring 
were fairly massed. Such a close aggregation of fish can rarely be seen in fresh water. They 
had evidently followed up along the outer edge of the tailrace until they could go no farther. 
Again, on the outer side of the last spillway in use, which was about 700 feet from the power house, 
there were considerable numbers of herring. From this point to the Illinois shore, a distance of 
about two-thirds of a mile, not a single herring was in evidence. It was evident, therefore, that 
the herring had been guided by the moving water, so that they had in consequence assembled in 
such remarkable numbers on each flank of the stream below the open spillways, many more being 
guided to the eastward side by the strong current from the turbines. 
Opportunity to observe whether they could breast the strong current was favored by the 
fact that there were three closed spillways between three open on the east and nine open on the 
west; thus, there was a triangle of relatively slack water between two strong currents that met a 
short distance below. To the west of the westward current fish were abundant; to the east of the 
eastward current they were still more abundant; but in the triangle between not one fish could be 
seen. It was evident, therefore, that the power of the currents below the spillways proved an 
effective barrier to the lateral movements of the fish for some distance below the dam, otherwise 
not all of the fish would have been on the right side of one current and on the left side of the other. 
The powerful currents caused slight eddies on each side, so that the dead water at the foot of 
the dam on either side was continually being drawn into the spillway streams. The fish were also 
drawn in, and it was easily observed that the velocity of the streams made them perfectly helpless. 
As soon as they passed into this stream they were thrown up in the foam and spray and often hurled 
