KEOKUK DAM 
125 
dent that the question of the direct productivity of the moving waters of large 
streams merits further investigation. 
After many years of investigation of the Illinois River, Richardson (1921, p. 
374) concludes that: “Speaking generally, the richest sections of the river floor are 
those with the least average slope and the slowest current, and therefore with the 
most abundant sediments.” Again he says (p. 376): “In our opinion, and that of 
the most intelligent and observant fishermen, the lakes are the favorite feeding 
grounds of the larger and more common fishes, and this opinion is supported by the 
fact that the lakes have a more abundant food supply per acre and that the heaviest 
fish yields come from sections where the ratio of lake areas to river is greatest.” 
Richardson estimates the productivity of the lakes and backwaters, as compared 
with the river, at about 2 to 1 (289 pounds of fish per acre in lakes and backwaters, 
and 141 pounds per acre in rivers, p. 469). 
Whatever may be the general superiority of slack waters over flowing waters in 
respect of biological productivity, it seems, from the studies of Galtsoff, that Lake 
Keokuk, although possessing something of the character and the advantages of a 
lake, is nevertheless not now to be given high rank as a lake. A similar inference 
may be made from the study of the commercial fisheries treated in the companion 
report. (Coker, 1930). Lake Keokuk, of course, is still immature as a biological 
plantation, and its final state can not be foretold, but in any case it is not in high 
degree free from many of the vicissitudes of river areas. 
It has been assumed that an increase of organisms constituting fish food would 
mean an increase of fish, but even this conclusion has been questioned by the author- 
ity who has devoted the most study to the ecology of the fishes of the interior waters 
of the United States. Forbes and Richardson (1914, p. 494), referring to an increase 
of organic life in the Illinois River, state: 
The fisheries of the stream should feel the effects of this greater abundance of this important 
element of fish food; provided, it must be added, that the plankton supply is really at any time a 
limiting element in the production of fishes, such that we may amend the aphorism, given on 
another page, to the form: “The more plankton, the more fish.” It will, however, be a long time, 
in the writers’ judgment, before the whole economy of fish production in our streams is so thor- 
oughly understood that such a statement will be warranted. 
Going even further than this, Juday and Wagner (1909, p. 21) have suggested 
that an unusually large amount of plankton in a lake might be detrimental to fishes 
because of the reduction of oxygen resulting from decay. It is evident that more 
knowledge on the questions involved is needed, but it is probable that rivers, at 
least, are improved as fish habitats by an increase in their content of food for fish. 
SPAWNING GROUNDS 
The fresh-water fishes, in general, are believed to spawn in shallow water. 
Examination of virtually all of the literature on the breeding habits of fishes occur- 
ring in the Mississippi River confirms this view for the species that have been 
observed at spawning time. 12 A great proportion of the newly submerged areas of 
Keokuk Lake are mostly shallow, and it is a reasonable expectation that these areas 
will make the lake a nursery for fish, which will help to stock not only the lake but 
to some extent the section of river above and possibly that below, also. The ques- 
tion may be raised whether or not the lake would have been biologically more pro- 
I! The breeding habits of the river herring of the Mississippi, the paddlefish, and the drum are not known. 
