112 
BULLETIN OF THE BUREAU OF FISHERIES 
river below. On the first one dropped into the head bay, too much cork had been 
tied and it did not submerge. Two others disappeared, and it is not known whether 
they went down. Two more evidently went down because the corks were found 
below. A sixth fish was put through and picked up below entirely uninjured and 
lively. This one was 72 centimeters (28 K inches) over all, and the piece of cork tied 
to its snout was 7 }{ by 4 % by 2% centimeters; it had been dropped into the head bay 
above unit 8 and carried down by a strong whirlpool. 
On August 29 two more paddlefish of about the same size and with slightly 
larger pieces of cork were put through in the same manner and picked up swimming 
and uninjured. 
With little hope of success, two attempts were made to test whether fish are 
hurt while trying to ascend the draft tubes. Paddlefish were staked out in the tail- 
race by means of a long line tied to the tail ; but the line repeatedly became entangled 
in something at the bottom of the tailrace, and the effort was abandoned. 
DISCUSSION OF EVIDENCE AND CONCLUSION 
The net results of the experimentation and observation are negative. The 
fishes dropped over the dam and put through the turbines escaped remarkably well, 
considering how they were hampered, particularly as the worst-looking places were 
selected purposely. Furthermore, the injuries received were to various parts of the 
bodies instead of being confined to the heads. It seems entirely possible that fish 
should ascend the draft tubes to the turbines, the velocity of the water being only 
about 9 miles immediately under the wheel and considerably less than 3 miles at the 
outlet. (Mississippi River Power Co., 1913, p. 32.) But, though the wheels move at 
a considerable velocity, the portions of them that would strike an ascending fish are 
broadly rounded, and it seems improbable that the injuries received could be inflicted 
by such a surface. In spite of these negative indications it is possible that further 
work would show that fish are sometimes hurt in one of the ways suggested. Paddle- 
fish, at least, are damaged in substantial numbers, and it is desirable that the cause 
be ascertained. There remains the possibility that the fish are injured in attempting 
to pass between some of the old pilings that, for a long time, at least, remained sub- 
merged about the raceway below the power house. If, while swimming abreast of 
the current, a fish should attempt to pass between two closely approximated piles, 
it is conceivable that the force of the current against the body of the fish would 
wrench the bill off as readily as one could break the bill by inserting it between two 
posts and moving the fish sharply to one side. 
EFFECTS OF THE DAM UPON CONDITIONS IN THE RIVER BELOW 
BOTTOM CONDITIONS 
The bottom material at and near Keokuk, below the site of the dam, as shown 
by Chart No. 136 of the Mississippi River Commission, was rock and sand with a 
little gravel and clay near the banks. These conditions were not changed by the 
dam. except that some sand may have been washed out right at its base. Places 
reported to have a bottom of mud were found by dredging (in April and May, 1916) 
to have sand, with occasionally molluscan remains and sometimes clay pellets. The 
changes in the character of bottoms above the dam must be pronounced and sig- 
nificant, but opportunity has not occurred for the investigation of such conditions. 
Before the dam was built the bottom in the rapids was described by Clark (1911) 
as “solid rock bottom all the way across.” He said, furthermore: 
