character or reservoir bottom, whether 

 highly organic or inorganic, on the physi- 

 cal and chemical quality of water entering 

 the reservoir, wind action to provide 

 circulatory currents, and on the point and 

 depth of water withdrawal from the reser- 

 voir. Adverse water quality factors in 

 regard to fish life that may arise from 

 water impoundment are: High water tempera- 

 ture; low dissolved oxygen; high or low 

 hydrogen ion (pH) concentration; excessive 

 carbon dioxide, ammonia and hydrogen sul- 

 fide from organic decomposition, siltra- 

 tion, and, accumulation of trace elements 

 that may be toxic to fish or their food 

 supply, such as copper, lead, selenium, 

 and zinc. Favorable water quality effects 

 that may arise from impoundment are: a 

 decrease in the downstream water tempera- 

 ture in the warm season and an increase in 

 the winter; increase in downstream flow, 

 during the normal low period, that will 

 more effectively dilute pollutants, and a 

 reduction in stream turbidity. Release of 

 impounded water will affect the stream 

 quality for some distance below the dam, 

 depending upon the water turbulence, air 

 temperatures, and the depth of water with- 

 drawal from behind the dam. References 

 (21-23) discuss the effects on water qual- 

 ity of impoundments in the Tennessee Valley 

 Authority reservoirs and in the Catawba 

 River, South Carolina. 



Return Flows from Irrigation 



In the irrigation of land, it is 

 necessary that the soil be well-drained so 

 that the plant roots do not become water 

 sick and so that salts do not accumulate 

 at the soil surface. A favorable salt 

 balance is attained when the drainage water 

 has a higher salt content than the input 

 water (_15 ) . Most irrigation projects are 

 provided with drains or waste-ways which 

 control the direction of ground water move- 

 ment in the root zone by returning excess 

 ground and irrigation waters to a receiving 

 strejim. 



The amount of water required for 

 irrigation varies from less than two to 

 more than 10 acre-feet of water applied per 

 acre per year (J^). Of this applied water, 

 from 20 to 60 percent may find its way back 

 to the stream as return flow. 



These return flow waters are more 

 mineralized cind have different physical 



properties from the input waters. Their 

 return to a stream will produce marked 

 water quality changes if the quantity of 

 return flow in relation to stream flow 

 is significant. Some return flow can be 

 expected throughout the year with the 

 majority occurring at the height of the 

 irrigation season. 



Domestic Sewage and Industrial Wastes 



The quantity of wastes discharged to 

 to inland waters is continually increasing. 

 Their content of polluting material is 

 under surveillance by, and is in the pro- 

 cess of being controlled by, water pollu- 

 tion control agencies. Uncontrolled 

 discharge of these waste waters has, in 

 many instances, caused serious impairment 

 in water quality to the extent that fish 

 life could not exist. It is to be expected 

 that these waste waters will have an in- 

 creased reduction in their deliterious 

 effect on the receiving streams as waste 

 treatment and other control processes 

 become more common. 



Soil Erosion 



Poor land management practices, in 

 the form of overgrazing or improper culti- 

 vation, together with logging, mining or 

 construction activities that do not control 

 soil erosion, frequently impart so much 

 silt to a stream that all other forms of 

 water quality impairment become minor in 

 comparison. A change in vegetation, such 

 as from coniferous to deciduous trees, will 

 frequently result in an increase in the 

 water color. 



WATER QUALITY EFFECTS ON FISH LIFE 



Water quality affects anadromous 

 fishes in different ways. It may, if 

 adverse, discourage the adults in their 

 upstream migration; kill them by toxicity 

 or disease before they reach the spawning 

 grounds; cause them to not spawn when at 

 the spawning beds; destroy their eggs by 

 providing an environment unfavorable for 

 hatching; or it may cause the newly hatched 

 fish to die through destruction of the 

 young fish itself or its food supply. A 

 search of the literature for specific water 

 quality constituents and their effect on 

 anadromous fishes is not very enlightening. 

 Different species of fish and the seime fish 



22 



