IT ORTH WESTERN LAKES OF THE UNITED STATES. 
53 
The purpose of the investigation was to extend to these lakes an examina- 
tion similar to the one that had been carried out on the Wisconsin lakes (Birge and 
Juday, 1911). Some of the methods, however, especially those for taking samples 
and plankton catches, had to be changed, as the lakes were much deeper. All of 
the results have been calculated similarly to those for the Wisconsin lakes in order 
that comparisons may easily be made. In most cases only one set of samples was 
secured from each lake, but these were taken during July and August, when they 
are most valuable, because the greatest variations of gas and thermal conditions 
exist at that time and the plankton is most abundant. Several of the more im- 
portant lakes — Pend Oreille, Hayden, and Coeur d’Alene — were sampled two or 
three times to give some data on the variation during these months. When these 
results are compared with those obtained from the investigation on the Wisconsin 
lakes, the seasonal changes for the remainder of the year can be deduced. 
The lakes studied vary in depth from Crater, 1,996 feet, the deepest known 
lake in the United States, to very shallow ones, such as Henry, 6 feet. The inves- 
tigation includes some very large lakes — such as Pend Oreille, Tahoe, Klamath, 
Chelan, Washington, Coeur d’Alene — and many smaller ones. All of the lakes 
except Crater and Tahoe are the result of glacial action. Several have no large 
outlets, and some, like Crater, have no outlet or inlet. Lakes Tahoe, Chelan, 
Pend Oreille, Coeur d’Alene, Washington, Bear, and Priest have several inlets 
and give rise to quite large rivers as their outlets. 
The report includes so many data that it is impossible to discuss them all, but 
they should be of great value to those who may wish to continue the study and to 
those interested in stocking the lakes with the fish best adapted to each lake. 
In carrying on the work the investigators were aided greatly by the Spokane 
Chamber of Commerce, by the State and county fish and game wardens of Idaho 
and Washington, and by business men and others who donated both time and use 
of boats. These and many other favors were duly appreciated, and it is hoped 
that this work may repay, at least in part, all who assisted. The authors are also 
indebted to the Wisconsin Geological and Natural History Survey for use of appa- 
ratus; to Dr. A. S. Pearse, of the zoology department of the University of Wisconsin, 
for identifying several amphipods; to Prof. G. M. Smith, of the botany department 
of the University of Wisconsin, for identifying many algas ; and to Dr. E. A. Birge and 
Mr. Chancey Juday, of the Wisconsin Geological and Natural History Survey, for 
advice in the work. Mr. Juday has also spent a great deal of time revising the 
biological part of the report. 
MAPS. 
The map of eastern Washington and Idaho and the one of western Washington 
show the location of the lakes studied in those States. (See figs. 7 and 18, pp. 77 
and 97.) The maps of Coeur d’Alene, Pend Oreille, Priest and Upper Priest Lakes 
(figs. 9, 14, and 17, pp. 82, 91, and 94, respectively) were copied from county maps. 
The soundings were located only roughly from the boat, but since this is the only 
information available concerning the depths of these lakes, it is shown on the maps. 
The dots locate the soundings; the depth is given in meters. 
