80 
bulletin of the bureau of fisheries. 
Since the thermometer used on Lake Chelan in 1911 read 4° C. on the other 
deep lakes, agreeing with the later standardized thermometers, it probably gave 
the correct bottom temperature of Chelan as 5.9° C. at 458 m. The 1913 tempera- 
tures were not taken at the same place. The deepest place (458 m.) was very 
small and in a narrow part of the lake. A spring entering near that place could 
have warmed the bottom water. A possible explanation of the higher temperature 
is that the bottom of the lake at this depth is warmer than the water and so gives 
up heat to the lower strata of water. This explanation is supported by the fact 
that the bottom temperature (with the thermometer touching the bottom) is 0.3° 
C. higher than the next two temperatures above the bottom. 
The water showed a high degree of transparency, since the white disk did not 
disappear from view until a depth of 14.25 m. was reached. 
The maximum number of organisms was obtained in the 0-10 m. stratum. 
A relatively large number of Crustacea was found in every stratum above 50 m. 
The maximum number of Chydorus sphxricus was between 150 and 200 m. Alm ost 
70 per cent of the Crustacea in the lake were Diaptomus; 21.6 per cent, Cyclops 
bicuspidatus; and the remainder, Daphnia pulex and Bosmina longispina. Two- 
fifths of the Diaptomus, one-fourth of the Cyclops, and one-third of the Daphnia 
and Bosmina were in the 0-10 m. stratum. (See Table 12, p. 123.) Nauplii were 
found in very small numbers, with the maximum number per cubic meter of water 
between 30 and 50 m. No rotifers were found in the limnetic catches. Ceratium 
was found chiefly in the upper 40 m. The diatom Melosira was found below 40 
m., and Asterionella was confined to the upper 100 m. 
CLEAR LAKE, WASH. 
This is a shallow lake with the exception of a deep hole at one end. The lower 
end of the lake is a shallow marsh. There is no tributary stream, so the lake must 
depend on rainfall, seepage, and springs for its water supply. 
Figure 8 shows the distribution of the plankton and the relation to the 
chemical conditions of the water. The Protozoa are abundant and show the typical 
form of distribution with the greatest numbers in the upper zone, 0 to 5 m. It will 
be noticed that the Cladocera and the Copepoda have moved up from the thermocline 
to a place near the surface and that the nauplii are not in the surface zone, but 
just below it. In other lakes these forms are not found in the warmer waters but 
are found in the transitional zone. In this lake the upper water is distinctly alka- 
line and this may have some effect; the same condition is noticed in Silver Lake. 
LAKE COEUR D’ALENE, IDAHO. 
This is the second largest lake in Idaho and, although comparatively narrow, 
it is 51.8 km. (32.2 miles) long. The elevation of the surface is 647.5 m. (2,124 feet), 
with a maximum variation of level of 3.7 m. (12 feet) . (See fig. 9.) The forest comes 
down to the water’s edge along the greater part of the very irregular shore line. 
The surrounding hills are not very high, and the valleys that run out from the 
lake are not very deep or precipitous. At the southern end, or head, the lake is fed 
by the St. Joe River, and at Harrison it receives the muddy waters of the Coeur 
d’Alene River, which drains an immense area, including the famous Coeur d’Alene 
mining district. These waters are so laden with silt that they may be traced far 
out into the clear water of the lake, the bottom of which shows the effect of the 
