448 
its own influx of tributary water from Quiver Creek, is the most 
liable of all the backwaters examined by us to hydrographic 
disturbance. It is therefore not surprising that in this year of 
extreme disturbance we should find marked depression for a 
long period in this lake. The total movement in levels in 1898 
is 67.2 ft. (see table p. 163), 44 per cent. above the average. Of 
this, 50.8 ft. fall in the 8 months of depressed production, that 
is, 76 per cent. of the movement occurs in 67 per cent. of the 
time. To this relative excess of fluctuation in levels, and proba- 
bly to large access of local flood and spring water, we must at- 
tribute the low production in Quiver Lake in these months. 
Thompson’s Lake has an average production of 5.06 cm.’, 
or, if all collections are averaged, 5.71 cm.*, 39 and 28 per cent. 
below the respective averages for all years (see table, p. 429). 
Not only is the general average below normal, but all of the 
menthly averages, save only those of January (7.22) and De- 
cember (3.58), are likewise deficient by from 2 to 88 per cent. 
The large January production is the largest plankton content 
in this month in any year or locality, and accompanies an 
invasion and impounding of sewage-laden river waters in the 
lake (cf. Pl. XLV. and L.). 
The cause of the low production throughout the remainder 
of the year is again to be found in the hydrographic conditions. 
During 8 months of the year (at levelsabove 6 ft., see Pl. XX XIX.) 
the lake is swept by a gentle current entering at the northern 
end and discharging to the channel at the lower. There is, 
thus, in this year more than the usual run-off, not only of or- 
ganic matters in solution and suspension, received with the 
waters of ingress, but also those developed in its impounded 
waters or about its shores. This tends to impoverish the 
waters, and interferes with the accumulation and flux of or- 
ganic matter in the plankton which manifested itself in such 
amplitude in the low water of the preceding year (Pl. XXX- 
VIII). Toa much less extent than in Quiver Lake is the de- 
pressing effect of flood waters seen in the broader expanse of 
this body of water. While in the former the production in 
