567 
There is thus, in general, a correspondence between plank- 
ton production and the product of the fisheries in that the d/- 
rection of movement in both is usually the same. They rise or 
fall together. If we compare the changes of the product of the 
fisheries with those of the sum of plankton production in chan- 
nel and backwaters, as given in the table on page 565, we see 
that the direction of the change is the same in both from year to 
year in every instance in 1894-1898. If similar comparisons 
are made of the product of the fisheries and plankton produc- 
tion in channel or backwaters alone, or in total discharge, we 
find that in three cases out of four the direction of the change 
is the same in both. It is also generally, true that years in 
which plankton production is below the average are also ones 
in which the product of the fisheries falls below the mean. 
Plankton production at Havana, provided a similar plank- 
ton content is maintained until the run-off reaches the mouth 
of the river, would result in an average discharge of 67,750 
cubic meters of plankton, equivalent in weight to somewhat 
more than 149,050,000 pounds, or 15 times the annual produe- 
tion of fish. To this wastage of organic matter, which in great 
part is permanently lost to the drainage basin of the Illinois, 
should be added the unutilized nitrogen and other food elements 
in suspension and solution which escape with the run-off, es- 
pecially of flood waters (see Table X.). 
How shall this waste be prevented and the plankton be 
turned into marketable fish? The problem is a complex one, 
but the results of this investigation should contribute towards 
its solution. The first step will be to impound the richly fer- 
tilized flood waters and thus to afford time for the utilization 
of their food elements by the developing. plankton, which by 
various chains of food relations is joined to marketable fish. 
An illustration of the productive possibilities of impounded 
Spoon River floods is seen in Phelps Lake, our richest plankton 
station, and also the home of great numbers of young fish. 
Thompson’s Lake, another impounding backwater, not only 
breeds an abundant plankton but contributes no insignificant 
