turbidities for short periods, a fortunate adaptation 

 for river species. Fish productivity is ultimately 

 dependent upon plant life and a good bottom 

 fauna. There can be little of either above 200 JTU 

 if that turbidity is maintained continuously. The 

 Aquatic Life Advisory Committee of the Ohio 

 River Valley Water Sanitation Commission 

 (ORSANCO) Second Progress Report (1956) 

 points out that fish withstand turbidities of 5,000 

 mg/1 or more with no direct harmful results, but 

 the productivity of the bottom areas is very low 

 and the fish populations are small. 



TABLE III-2. Average Turbidities Found To Be 

 Fatal to Fish 



Length of Turbidity 



Species exposure (days) (mg/l) 



Large mouth bass 7.6 101,000 



Pumpkin seed sunfish 13 69,000 



Channel catfish 9.3 85,000 



Blacl< bullhead 17 222,000 



Golden shiner 7.1 166,000 



Ellis (1937) summarized the results of 2,344 

 light penetration determinations made at 585 sta- 

 tions on streams throughout the United States. The 

 determinations were made of the millionth inten- 

 sity depth (m.i.d.), which is the depth in milli- 

 meters of water of the given turbidity required to 

 screen out 99.9999 percent of the light entering at 

 the surface. A photoelectric apparatus described 

 by Ellis (1934b) was used and determinations 

 were made after filtering the water through bolting 

 silk. 



The turbidity of rivers varies widely in different 

 parts of the country. Ellis (1937) defined clear 

 streams as those with a m.i.d. of 5.00 to infinity; 

 cloudy streams, 4.90-1.00 meters; turbid, 0.99- 

 0.50; very turbid, 0.49-0.30; muddy, 0.29-0.15; 

 very muddy, 0.14-0.00 meters. 



In Mississippi River side channels and flowing 

 stream tributaries with good fish fauna, 4 percent 

 were clear, 1 1 percent cloudy, 3 percent were very 

 muddy. In these waters, with medium, poor, or no 

 fish fauna 1 percent were clear, 1 8 percent cloudy, 

 11 percent turbid, 14 percent very turbid, 38 per- 

 cent muddy, and 18 percent very muddy. 



Based on 6,000 light penetration determinations 

 on inland streams, he concluded that, for good pro- 

 duction of fish and aquatic life, the silt load of 

 these streams should be reduced so that the mil- 

 lionth intensity depth would be greater than 5 

 meters. 



Good farming practices can do a great deal to 

 prevent silt from reaching streams and lakes. Road 

 building and housing development projects, placer 



mining, strip irtining, coal and gravel washing, and 

 unprotected road cuts are important sources of 

 turbidity that can be reduced with planning, good 

 housekeeping, and regulation. 



Natural turbidities within watersheds should be 

 determined. For example, in some Western States 

 many streams have a turbidity below 25 JTU for 

 most of the year. In those states, the water pollu- 

 tion control agency might specify that no wastes 

 should be discharged which would raise the tur- 

 bidity of the receiving water above 25 JTU. 



From the above discussion it can be seen that 

 natural turbidity varies greatly in different parts of 

 the country. 



Recommendation: Turbidity in the receiving water 

 due to a discharge should not exceed 50 JTU in warm- 

 water streams or 10 JTU in cold-water streams. 



There should be no discharge to warm-water lakes 

 which will cause turbidities exceeding 25 Jackson Units. 

 The turbidity of cold-water or oligotrophic lakes should 

 not exceed 10 units. 



Settleable solids 



Settleable solids include both inorganic and or- 

 ganic materials. The inorganic components include 

 sand, silt, and clay originating from such sources 

 as erosion, placer mining, mine tailing wastes, strip 

 mining, gravel washing, dusts from coal washeries, 

 loose soils from freshly plowed farm lands, high- 

 way, and building projects. The organic fraction 

 includes such setrieable materials as greases, oils, 

 tars, animal and vegetable fats, paper mill fibers, 

 synthetic plastic fibers, sawdust, hair, greases from 

 tanneries, and various settleable materials from city 

 sewers. These solids may settle out rapidly and 

 bottom deposits are often a mixture of both inor- 

 ganic and organic solids. They may adversely af- 

 fect fisheries by covering the bottom of the stream 

 or lake with a blanket of material that destroys the 

 bottom fauna or the spawning grounds of fish. 

 Deposits containing organic materials may deplete 

 bottom oxygen supplies and produce hydrogen 

 sulfide, carbon dioxide, methane, or other noxious 

 gases. 



Some settleable solids may cause damage by 

 mechanical action. 



Water Quality Criteria for European Freshwater 

 Fish (European Inland Fisheries Advisory Com- 

 mission, 1964) discusses chemicaDy inert solids 

 in waters that are otherwise satisfactory for the 

 maintenance of freshwater fisheries. It is indicated 

 that good or moderate fisheries can be maintained 

 in waters that normally contain 25 to 80 mg/1 sus- 

 pended solids, but that the yield of fish might be 



47 



