366 
BULLETIN OF BUREAU OF FISHERIES 
general use with reasonable expense, if all parties concerned would cooperate. To 
obtain this cooperation, it is necessary to understand the situation and to judge it 
fairly. Much confusion and misunderstanding has arisen in attempts to define the 
extent of pollution and to place the responsibility for damage to fisheries, because of 
the lack of available information on the conditions to be defined. 
In the present paper findings from the widely scattered scientific literature sup- 
plemented by the experimental and field work of various agencies have been brought 
together covering (1) the conditions which should be maintained if good fish faunae 
are to thrive, and (2) the specific effects of various types and components of effluents 
which now pollute our streams. 
It is hoped that the use of this information will make possible the definition of 
undesirable conditions with fairness both to the industrialist, who must use water 
and streams, and to the citizen, who is entitled to enjoy these same streams. 
With the limits of both the required stream conditions and of the pollutant 
lethalities better understood, corrective measures can be recommended intelligently, 
for remedial action can only be instituted when the cause and the severity of the 
pollution are known. The United States Bureau of Fisheries is engaged at present 
in such investigations based on findings presented here. 
STREAM POLLUTANTS AND AQUATIC ENVIRONMENT 
PHYSICAL AND CHEMICAL CHARACTERISTICS OF WATERS SUITABLE 
FOR FRESH-WATER STREAM FISHES 
The various effluents, municipal, industrial, and otherwise which comprise col- 
lectively stream pollutants may be detrimental to fishes and other aquatic life either 
indirectly through quantitative alterations in those substances which give fresh 
waters their inherent characteristics, as dissolved oxygen, carbonates, and hydrogen 
ions, or directly because of specific physiological and toxic effects on the aquatic 
organisms themselves. Many effluents are of complex composition, however, and 
are harmful to aquatic life through both changes in the aquatic environment and 
through definite toxic actions. Therefore, in determining the effects of stream 
pollutants on aquatic biota and particularly on fishes, it has been necessary to study 
both the modifications in the environment and the specific physiological actions 
attributable to the different pollutants. 
The many substances which are carried in solution and suspension by a stream, 
collectively determine whether the waters of that stream in themselves present con- 
ditions favorable or unfavorable for fishes and other aquatic organisms; and any 
individual fish in the stream is affected not only directly by these substances, but 
indirectly through their action on other forms of aquatic life which comprise in a 
very restricted environment the food, the enemies, and the competitors of the par- 
ticular individual. The definition of the amounts of these substances which should 
be present in water in order to maintain a suitable environment for fishes, or which 
may be tolerated by fishes under favorable conditions, is therefore much more 
involved than the designation of standards for water for human consumption, which 
concern but a single, air-breathing, non-aquatic animal, man. 
