natural waters; (2) determining by laboratory 

 studies the relative sensitivity of organisms to 

 various environmental factors, and ranges which 

 are tolerable and favorable; (3) determining by 

 means of different bioassay studies the behavioral, 

 physiological, and other responses of organisms to 

 potential toxicants and concentrations of these 

 materials which are not harmful under continuous 

 exposure; and (4) testing laboratory findings in 

 the field to determine their adequacy for the pro- 

 tection of aquatic and wildlife resources. 



In approaching this problem of protecting our 

 aquatic and wildlife resources, it must also be 

 realized that: (1) certain natural complexes of 

 dissolved materials to which aquatic organisms 

 have become adapted are favorable whereas other 

 concentrations or compositions may not be; (2) 

 unnatural materials added by man can be unfa- 

 vorable; (3) altering the amounts of substances 

 normally found in the environment can be harm- 

 ful; (4) toxicity is a quantitative term — any mate- 

 rial becomes toxic when its concentration exceeds 

 certain levels. It is essential, also, to realize that 

 requirements must be maintained throughout pe- 

 riods of low water, maximum discharge, maximum 

 temperature, minimum DO, variations in pH, 

 turbidity, salinity, etc. Further, it should be under- 

 stood that: (1) unfavorable conditions which may 

 be resisted for long periods by adults may be en- 

 tirely unfavorable for the survival of the species; 

 (2) conditions need to be unfavorable for only a 

 few hours to eliminate a population or group of 

 species; and (3) levels of environmental factors 

 and concentrations of toxicants that appear to 

 cause no harm during a few hours of exposure 

 may be intolerable for extended periods or for 

 recurring short-term exposures. 



In defining water quality requirements for 

 aquatic life and wildlife, it is necessary to define 

 the extreme upper and lower limits of the various 

 environmental factors as well as the optimum 

 values. These extremes are outer limits and con- 

 stitute the minimum objectives to be obtained in 

 the improvement of waters for aquatic life. It is 

 not the intention of the Subcommittee that such 

 levels are to be considered as satisfactory. Fur- 

 ther, it is stressed that waters of higher quality 

 should not be degraded towards approximation of 

 the extremes. For example, the dissolved oxygen 

 content of water should be near saturation for best 

 production. The lower limits for oxygen indicated 

 in the report, therefore, represents the objective to 

 be obtained in the improvement of water, and not 

 the level to which good waters may be lowered. 



It is essential that the various recommendations be 

 considered in context with the body of the report, 

 taking due consideration of the variability of local 

 conditions and native biota. 



Within the United States there are great varia- 

 tions in environmental conditions and in the flora 

 and fauna. The environmental requirements of the 

 biota are different not only for different regions but 

 for different portions of the same region. Overlying 

 these differences are seasonal changes and daily 

 variations that have become essential factors in the 

 environment. Ideally, therefore, water quality cri- 

 teria for aquatic life and wildlife should take into 

 consideration local variations in requirements, sea- 

 sonal changes, and daily variations. They should 

 be national in scope. They should be applicable to 

 streams of various size and character, to all types 

 of lakes, to reservoirs, estuaries, and coastal 

 waters. 



It is obvious that more research is needed on the 

 character, conditions, and interrelations in fresh 

 water, marine, and estuarine ecosystems which are 

 subjected to degradation or alteration as well as on 

 the physiological requirements and tolerances of 

 the various species involved in these different eco- 

 systems. This need must be satisfied for the estab- 

 lishing of sound criteria to maintain and preserve 

 aquatic resources and to permit the most economi- 

 cal and productive use of these resources by man. 



Further, water quality requirements must be 

 expressed so as to allow for environmental modifi- 

 cations where such modifications are justifiable 

 and deemed to be in the public interest. 



All these factors have been considered in de- 

 veloping the following recommended water quality 

 requirements for aquatic life. 



It is the purpose of this document to define the 

 water quality requirements which must be met to 

 insure a favorable environment for fish, other 

 aquatic life, and wildlife. This report will do this 

 by identifying those aspects of water quality that 

 are most important in the light of current knowl- 

 edge and quantifying them where possible. Where 

 quantification is not yet possible, narrative guide- 

 lines will be offered. There is no doubt that the 

 water quality requirements contained herein must 

 be reviewed periodically and updated in the light 

 of additional and improved scientific data. The 

 recommendations given in this report are consid- 

 ered to be satisfactory for aquatic life. In all 

 instances where natural conditions fall outside the 

 recommended ranges, this environment may be 

 marginal and should not be changed in such a way 

 as to make it more unfavorable. 



30 



