440 
In these lakes at levels prevalent in this year the impounding 
or reservoir function is at its height. The higher levels reduce 
the relative proportion of creek and spring water, and the ab- 
sence of extreme high water cuts off to large extent the cur- 
rent of general overflow through the lakes. Accordingly, pro- 
duction here in the year as a whole exceeds the mean of all 
monthly averages by 25 (Quiver) and 26 (Dogfish) per cent., 
and exceeds the mean of the respective monthly averages in 8 
and 7 of the 12 months. In the case of Thompson’s Lake, on the 
other hand, the hydrographic conditions are such that its pre- 
dominantly reservoir function is interfered with as each recur- 
rent flood passes the level of 6 ft. and starts the current of 
channel water in at the northern, and out at the southern, end 
of the lake (Pl. II.). Accordingly production in this lake falls 
below the average of all monthly averages by 24 per cent., and 
the individual monthly means are likewise deficient in 9 of the 
12 cases. 
In Flag Lake the production (8.31 or 13.83 em.’ per m.*) is 
10 per cent. below the mean of all monthly averages, or 21 per 
cent. above that of all collections, and exceeds the means of the 
monthly averages in 6 of the 12 months. The accumulated 
vegetation in and about this lake, and the moderate levels 
which develop the reservoir function of the area without per- 
mitting any current of overflow through it tend to keep up the 
level of production. It is in considerable excess of that in sub- 
sequent years, but falls below that of the exceptional condi- 
tions of the preceding autumn, discussed on page 385. 
The moderate levels free Phelps Lake from currents of 
overflow and increase its impounding function, and we find 
here, accordingly, the largest production recorded in any of the 
backwaters in this year. The fact that the production (14.74 
cm.” per m.") falls 34 per cent. below the mean of all monthly 
averages for the lake and is deficientin 6 of the 12 months, may 
perhaps be due in part to the fact that in the previous year the 
lake had been a cultivated corn field and had not therefore been 
seeded by the spores and winter eggs of planktonts left on the 
