NORTHWESTERN LAKES OF THE UNITED STATES. 
83 
During the time of our visit to the lake the Milwaukee Railroad was building 
a grade up the St. Joe River and was sluicing the earth from the cuts into the water. 
The effect of this was noticeable 75 miles below at the lower end of the lake, where 
for years no trout had been caught; but this year the muddy water had driven them 
down to the head or source of the Spokane River, where they were being taken. 
All trout fishing had ceased at the upper end of the lake, and in the St. Joe River as 
well, except above the point where the grade was being constructed. 
In all of the deeper lakes already considered the Crustacea were found in greatest 
abundance above the thermocline. In Lake Coeur d’Alene the thermocline was 
situated in the 10-12 m. stratum, and just as large numbers of Crustacea were found 
below this region as above. Diaphanosoma hrachyurum was confined to the upper 
5 m. of the lake. (See Table 12, p. 124.) The maximum number of Cyclops bicolor 
per cubic meter of water was found in the 0-5 m. stratum, and this form was found in 
fairly large numbers throughout the lake. Bosmina longirostris var. brevicornis, 
constituting 24 per cent of the entire catch of Crustacea, was distributed throughout 
the lake, hut fully 45 per cent were found in the lower 10 m. of the lake, or below 
40 m. 
About one-half of the adult Crustacea were found above the thermocline, but 
the region above the thermocline — the epilimnion — was smaller than that below. 
There were 16,200 Crustacea per cubic meter of water in the 0-5 m. stratum of the 
lake and only 4,480 in the 5-10 m. stratum. In the 10-25 m. stratum there were 
12,590 Crustacea and below 30 m. 12,680. 
Nauplii were found in considerable numbers throughout the lake, especially 
below the thermocline. There were from 1,500 to 1,850 per cubic meter of water 
above the thermocline, but the maximum of 3,900 occurred in the 10-15 m. stratum. 
The rotifers consisted of Mastigocerca, which was confined to the 0-10 m. 
stratum of the lake. (See Table 12, p. 124.) The maximum number of 1,720 per 
cubic meter of water was found in the 0-5 m. stratum. 
The phytoplankton in the lake consisted of two diatoms, Tabellaria and Aste- 
rionella. Tabellaria was found entirely above 15 m., 43 per cent being in the 10-15 
m. stratum. The remainder was distributed uniformly through the 0-10 m. 
stratum. A few Asterionellas were found in the 0-10 m. stratum of the lake and 
58 per cent of the total number in the 10-15 m. stratum. No diatoms were found 
in the 20-45 m. stratum, but 31 per cent of the Asterionellas were found in the 
50-55 m. stratum. 
At the upper end of the lake, near Harrison City, the plankton was not abun- 
dant, but it showed the typical distribution. The results at this station were not 
satisfactory, because the silt hindered the counting of the Protozoa and the diatoms. 
The tributary waters are rich in both of these forms, and they are no doubt repre- 
sented in the lake. 
A set of plankton catches was taken in the deepest part of the lajse. At this 
point, also, the plankton was scarce. The Crustacea were most abundant in the 
upper 5 m. of water. The rotifer Mastigocerca was confined to the upper 10 m., 
and nearly all of the algae were found in the upper 15 m. 
