401 
rise is 26.9 feet—sufficient to fill the channel for 81 miles. 
When we add to this the consideration that at levels above 6 
ft. water is continually passing through the lake with brief im- 
pounding, the length of channel filled by the run-off of this 
area must be considerably extended. 
The relationship of plankton production in this lake to the 
plankton content in channel waters in this year may be in- 
ferred from the yearly averages. Thompson’s Lake contained 
9 em.’ per m.* to 1.16 em.* in the river. The net result would 
therefore be an enrichment of the channel plankton in a 
ratio dependent upon the relative volumes of the mingling 
waters. No quantitative statement of this ratio is possible in 
the absence of data as to the run-off of Thompson’s Lake. Not 
only is the net result an increase in the channel plankton, but 
the monthly averages (see table between pp. 342 and 343) and 
the coincident or approximate individual collections (Tables 
IIL. and VIII.) in every instance exhibit a higher plankton con- 
tent in this lake than in channel waters. The monthly aver- 
ages range from 2 to 251 times greater in Thompson’s Lake 
than in the river—ratios within which most, if not all, of those 
of individual collections fall. The data all indicate that this 
impounded water of the lake breeds a plankton whose run-off, 
without exception throughout this year, enriched channel waters. 
The effect of invading and plankton-poor river waters upon 
the plankton content of the lake is not conclusively apparent 
in the data, since we have also to deal with the phenomenon 
of pulse-like changes in plankton content which are combined 
with other factors in affecting the movements in production. 
It may be significant of the diluent action of invading river 
water that plankton content falls in the lake with the first en- 
trance of the May-June, the July-August, the October, and the 
November floods (Pl. XXXVII.). The recovery in production 
follows promptly in each case with the impounding of the en- 
tering waters. Since, however, declines in content, as in June, 
July,and August, occur also when flood waters are not enter- 
ing, we cannot conclude that the decline upon this entrance is 
