457 
o1.9 ft. It is not so much the extent of movement in levels as it 
is distribution which produces this depression in production. 
Repetition of floods at relatively brief intervals is the cause of 
low production in channel waters in 1896. 
Not only is the mean production in the river below normal, 
but all of the monthly averages are likewise from 97 to 35 per 
cent. below their averages except those of April and December, 
which are 23 and 7 per cent. above. Hydrographic conditions in 
these two months of higher production are such as to favor in- 
crease in plankton, since in both cases there is a period of 6-8 
weeks of slowly declining levels with little or no interruption 
in which a more abundant plankton becomes established. 
The relation of production in the channel and the back- 
waters in 1896 is also very different from that in 1895. While 
in 1895, owing to low levels in general and to the prolongation 
of rising levels, the backwaters were contributing but a slight 
and interrupted run-off to the channel, and production, as shown 
in monthly averages, was in the case of backwaters examined 
predominantly lower than in the channel, we find in 1596, owing 
to higher levels, that there is more impounding, and, owing to 
the slow declines, a larger continuance of it and more run-off 
to the channel. There are, for example, 157 days of falling 
levels above 6 ft. distributed through 10 months, while impound- 
ing and run-off continues for 90 days more at lower levels and 
in decreased volume. Not only are backwaters thus contribut- 
ing to the channel for a much longer period in 1596, but their 
plankton content is predominantly higher than that in the 
channel. An examination of the relative production (see table 
on p. 436) reveals but 3 out of the 58 monthly averages of pro- 
duction in backwaters, excluding Spoon River, which are less 
than coincident production in the channel. These are for Dogtish 
and Quiver lakes in July, and forthelatter in September—both 
months of lowest water,and consequent predominance of creek 
and spring water in Quiver and of vegetation in both lakes. 
This relatively greater production in the backwaters is not due 
to increased absolute production as compared with 1895 except 
