418 
stages above 8 ft., 90 from Jan. 1 to Mar. 30, and 14 and 10 re- 
spectively in the floods of May-June, and August. Of the 114 
days there were 28 of levels above 10 ft., when, owing to run-off 
from Spoon River, a current passes through the lake to the 
river regardless, as a rule, of rising or falling water. In addi- 
tion there were 43 days of falling water when a run-off might 
be expected, making a total of only 71 days in this year in 
which there was any run-off to channel waters from this lake. 
The remaining 43 days of levels above 8 ft. were times of sta- 
tionary (20) or rising (23) water, when discharge from Phelps 
Lake was diminished or cut off. 
Of the 71 days of discharge, 61 fall in the winter, in Janua- 
ry-March, and 5 each in Juneand August, at times of depres- 
sion in production (Pl. XL.). Nevertheless, the plankton con- 
tent in Phelps Lake at all of these times greatly exceeds that in 
channel waters. The ratio of Illinois River and Phelps Lake 
plankton in Jannary is 1 to 189, in February, 1 to 607, in March, 
1 to 274, in the June flood, 1 to 4,and in the August rise, 1 to 7. 
These latter ratios are somewhat exceeded by those of the av- 
erage production for the year, 1.16 to 13.17 em., or 1 to 11. 
During the months of little or no discharge, April-December, 
production in the lake as shown in monthly averages is 4- to 
16U0-fold greater in Phelps than in the Illinois, the latter figure 
being reached in November and the other months averaging 
only 11-fold. 
Thus, this lake contributed to the enrichment of channel 
plankton for a relatively brief part of the year, and at all times 
produced a plankton greatly in excess of that in channel wa- 
ters. The sharp contrast between the poverty of channel wa- 
ters and the wealth of this lake is due to the impounding func- 
tion in the latter, and to the repeated flushings by storm waters 
of recent origin in the former. Full time for the normal utili- 
zation of the resources for growth of the plankton is permitted 
in the lake but not realized in the constantly replaced river 
water. 
This is the only year in which collections were made in 
