544 



Lake, where tributary creek and spring waters form a larger 

 proportion of the content of the lake, and 19 of the 30 are in 

 the low-water period, July-November, when the proportion of 

 tributary waters is greatest and the impounding function at its 

 lowest level, and vegetation at its height. Of the remaining 

 18 instances of deficiency, 6 are in Dogfish Lake, which is to 

 some extent under the influence of the hydrographic condi- 

 tions of Quiver Lake, and is likewise dominated by vegetation. 

 Three of the 6 cases of deficiency appear in July-August, in 

 the height of the dominance of vegetation and at times of 

 slight run-off. Two instances at the same season and under 

 similar conditions of vegetation and discharge appear in the 

 monthly averages of Flag Lake. In the monthly averages of 

 Thompson's Lake there are 8 instances of deficiency, but in half 

 of these the deficiency is less than 30 per cent. There are but 

 2 cases of deficiency in Phelps Lake, both at times when Spoon 

 River tributary water was passing through the lake. Further- 

 more, 33 of the total 48 instances of deficiency in production 

 in backwaters, as compared with channel, occur in July-De- 

 cember, during the low-water period of least run-off of im- 

 pounded backwaters, and of the remaining 15 instances during 

 the January-June period some probably result from insufficient 

 data, and others are found when the stagnation {Moina) pulse 

 of June, 1895, occurred in the river. 



We must, therefore, conclude that the greater part of the 

 backwaters predominantly bring to the channel in their run-off 

 a richer plankton than that with which their contributions are 

 mingled. The extent of this predominance and its changes 

 with the seasons and from year to year will be seen in the 

 table of monthly means following page 342. It is summarized 

 in the following table, which gives the mean plankton content 

 in channel waters for each month and the average of the 

 monthly means of the five backwaters. Quiver, Dogfish, Flag, 

 Thompson's and Phelps lakes, together with the ratios between 

 channel and backwater production in each month. 



An inspection of this table shows that during the colder 



