NORTHWESTERN LAKES OF THE UNITED STATES. 
Ill 
TEMPERATURES. 
Le Conte (1883, 1884) took a very complete series of temperatures of this lake 
August 11 to 18, 1873. He used a Six self -registering thermometer, which he 
compared with a standard and applied corrections. Juday (1907) determined the 
temperature to the depth of 425 feet in June, 1904. These are arranged in Table 8 
with our July 22, 1913, set for comparison. 
The low surface temperature (15.4° C.) would be expected in a large deep 
mountain lake with an elevation of 1,897 m. (6,225 feet). The temperature 
decreases gradually to 100 m., from which point to the bottom the temperature 
varies only a fraction of a degree. The bottom temperature was 4.1° C., or within 
0.1° C. (our limit of error) of the generally accepted temperature of water at its 
greatest density. Le Conte’s (1883, 1884) temperature of the bottom water is 4° C. 
Table 10. — Temperatures taken at various depths, Lake Tahoe, Calif., 1873, 1904, and 1913. 
Depth. 
August, 
1873. 1 
June, 
1904. > 
July 22, 
1913. 
Depth. 
August, 
1873. i 
June, 
1904. a 
July 22, 
1913. 
Feet. 
0 
16 
23 
25 
26 
29.5 
32.8 
50 
65.6 
75.0 
100 
125 
150 
M. 
0 
5 
7 
7.6 
10 
15 
20 
22.8 
25 
30 
46 
° F. 
67 
° F. 
60.75 
° F. 
59.8 
56.1 
55.2 
55 
54 
53 
52.3 
51.3 
Feet. 
200 
250 
300 
330 
400 
425 
480 
500 
600 
772 
M. 
61 
76 
91 
100 
122 
o F 
48 
47 
46 
45.5 
45 
° F. 
41.75 
° F. 
57 
41.25 
40.8 
40.8 
39.9 
44.5 
44 
43 
41 B 
63 
55.25 
152 
182 
244 
300 
400 
459 
501 
54.75 
50.3 
48.4 
39.5 
39.5 
55 
49.75 
46 
1,506 
39. 2 B 
50 
39. 4 B 
1 Le Conte (1883, 1884). a Juday (1907). 
PLANKTON. 
Both DapJinia longispina var. hyalina, form richardi, and Daphnia pulex were 
found and comprised the limnetic Cladocera. They did not occur in catches above 
50 m. These two forms constituted less than 1 per cent of the total number of 
plankton Crustacea. 
The maximum number of copepods per cubic meter of water was found in the 
0-10 m. stratum, where there were more than 6,000 Epischura and Diaptomi per 
cubic meter of water. Although the lake is more than 500 m. deep, almost one- 
fourth of the Crustacea (22.6 per cent) were found in the 0-10 m. stratum. There 
was a decrease in the number of Crustacea in the 10-30 m. stratum, with a rapid 
increase between 30 and 50 m. Below 50 m. the number decreased rapidly, and 
below 200 m. only a few were found. 
There were very few nauplii found in Lake Tahoe, and they were confined 
largely to the 0-10 m. stratum. About 67 per cent were in this region of the lake. 
(See Table 12, p. 133, and fig. 21.) They decreased very rapidly below 10 m., and 
none was found below 80 m. 
The only rotifier found was Noiholca longispina, which occurred in very small 
numbers and was confined to the upper 100 m. of the lake. 
