SALMON INVESTIGATIONS IN COLUMBIA RIVER BASIN IN 1896 
19 
The following temperatures were taken August 11, in Alturas Lake just beyond 
the bar at the mouth of the iulet. All are bottom temperatures except the first three. 
The first, second, third, and fourth were all taken at the same place, the others a short 
distance away: 
1. At surface 57° I 5. At depth of 72 feet 43° 
2. At depth of 24 feet 54 6. At depth of 96 feet . 40£ 
3. At depth of 48 feet 45 7. At depth of 102 feet 40J 
4. At depth of 90 feet - 40§ I 
Two series of temperatures at different depths were taken in Alturas Lake August 
11, between 3 p. m. and 6 p. m. These are shown on the temperature diagram on pre- 
ceding page. The series indicated by the crosses shows the bottom temperatures, 
obtained by starting near shore in 1 fathom and going outward into increasing depths. 
The circles on the continuous line indicate a vertical series taken near the middle of 
the lake, where the depth was 150 feet. It will be noticed that, after reaching a depth 
of 30 feet, the two series coincide exactly and that the temperature at the bottom iu 
the deepest part of this lake is but slightly, if at all, above that of fresh water at its 
greatest density, namely, 39°. 
A similar series was taken at Big Redfish Lake August 9, between 2.30 and 3.30 
p. m., the results of which are platted on the same diagram, an examination of which 
shows that this lake is, as a whole, considerably colder than Alturas Lake. Though 
the surface temperatures are nearly the same, the water in Big Redfish Lake is seen 
to grow colder much more rapidly as the depth increases. This is apparently due to 
the greater size and depth of Big Redfish Lake, the lower temperature of the inflowing 
water, and the greater protection afforded by the higher surrounding mountains. In 
both lakes, however, the temperature decreases rapidly until a depth of about 100 feet 
is reached, and beyond that depth the decrease is less than 2° in either case. 
These temperatures were taken with a Regretti Zambra deep-sea thermometer 
tripped by means of a messenger, and the results are believed to be reliable. The 
bottom temperatures which we took at these lakes in 1895 were taken with a Wilder 
protected thermometer, and we are now convinced that the results obtained are wholly 
unreliable whenever the depth exceeded a few feet. The thermometer can not be 
drawn up quickly enough to prevent the mercury from being warmed by tbe warmer 
water above. The few bottom temperatures given in the report of the work done on 
these Idaho lakes in 1895 are therefore worthless. 
SUMMARY OP OBSERVATIONS REGARDING THE REDFISH. 
Camp was established on the outlet of Alturas Lake July 11, and observations 
began on that date. The daily inspection of. the nets and the periodical examination 
of Alturas Creek and Salmon River were carried on essentially as during the season 
of 1895. Although gill nets could not be well placed until July 17, the opportunities 
for examining the stream make it certain that if any redfish had ascended to the lake 
between July 11 and 17 they would have been seen. 
Beginning with July 17, gill nets were kept constantly in the outlet of Alturas 
Lake, set in such manner as wholly to obstruct the stream to the ascent of fish. These 
nets were kept iu place until September 25, but not a single redfish, either of the 
large or small form, was caught in them. No redfish were seen in the outlet or else- 
where below Alturas Lake during the season. Small redfish appeared in the inlet in 
considerable numbers in August and September, but no large redfish were seen this 
year at any of the Redfish Lakes. 
