407 
interchange between lake and river. The average height for 
this year is 8.02 ft., the highest during our years of record. 
From Jan. 22 to July 15 river levels were above 6 ft., anda 
constant inflow of impounded water from bottom-lands above 
the lake, or through the slough when overflow ceased, continued 
with impounding in the lake and subsequent discharge from its 
southern end to the channel. The same conditions again 
prevailed from Oct. 30 till the end of the year, with an inter- 
ruption of 6 days in December. During the remaining parts of 
the year there was a constant wavering in levels which fa- 
vored frequent—in fact, no less than 21—reversals in the direc- 
tion of flow in the slough connecting the lake with the river. 
During the 134 days of low water there were 56 of falling levels 
in which the lake was discharging its plankton-laden water 
through the slough to the river, making a total of 287 in which 
it contributes to channel plankton to 78 in which, owing to low 
levels, it merely receives an inflow from the river. Moreover, 
the periods of greatest plankton production in the lake, during 
the vernal pulse, occur at times when the run-off from the lake 
is at its height, so that in this year all the hydrographic factors 
combine with the distribution of the plankton production to 
render this reservoir lake a feeder of the channel plankton. 
Though the differences in the plankton content are such that the 
actual enrichment per cubic meter may be less than in other 
years, the total run-off of plankton into the channel must com- 
pare favorably with that in any other year of our operations. 
The comparison of coincident collections shows in all cases 
but three, a greater plankton content in the lake than in 
river. The first of these is on April 5, at the height of the 
spring flood, when a considerable current sweeps through 
Thompson’s Lake and shortens the period of impounding, and 
thus reduces the time for the development of the plankton. 
The second instance is on June 21, on the decline of the acces- 
sory vernal pulse, which reaches a lower level in the lake 
(2.47) than in the river (2.88). This is one phase of a not un- 
common phenomenon in the plankton pulses of the backwaters. 
