lower than in waters containing 25 mg/l or less. 

 Waters normally containing 80 to 400 mg/l sus- 

 pended solids are unlikely to support good fresh- 

 water fisheries. 



Recommendation: Since it is known that even minor 

 deposits of settleable materials inhibit the growth of 

 normal stream or lake flora and fauna, it is recom- 

 mended that no settleable materials be added to these 

 waters in quantities that adversely affect the natural 

 biota. 



Color 



The color of water is attributed to substances 

 in solution after the suspensoids have been re- 

 moved. It may be of organic or mineral origin. 

 Organic sources are humic materials, peat, plank- 

 ton, rooted and floating aquatic plants, tannins, 

 etc. Inorganic sources are metallic substances such 

 as iron and manganese compounds and chemicals, 

 dyes, etc. Many industries discharge materials that 

 contribute to the color of water. Among them are 

 pulp and paper mills, textile mills, refineries, 

 manufacturers of chemicals and dyes, explosives, 

 nailworks, tanneries, etc. 



Standard Methods for the Examination of Water 

 and Wastewater, 12th edition (1965), describes 

 the standard platinum-cobalt method of determin- 

 ing color after centrifugation. The unit of color 

 considered as standard is the color produced by 

 one mg/l of platinum in water. Results are ex- 

 pressed as units of color. Color in excess of 50 

 units may limit photosynthesis and have a dele- 

 terious effect upon aquatic life, particularly phyto- 

 plankton, and the benthos. 



Water absorbs light differentially. A layer of 

 distilled water 1 meter in thickness absorbs 53 per- 

 cent of the solar radiation. It absorbs 30 percent of 

 the red-orange band (6,500 angstrom units) but 

 less than 5 percent of the blue (4,500 angstrom 

 units). These are the portions of the spectrum that 

 are absorbed and utilized to the greatest extent by 

 chlorophyll. The band at 7,500 angstrom units is 

 over 90 percent absorbed. 



Natural waters absorb far more light. The light 

 intensity at which the amount of oxygen produced 

 photosynthetically is balanced by the amount of 

 oxygen used for respiration in some submerged 

 vascular plants is 5% of full sunlight on clear 

 summer days. It is estimated that 25 to 50 percent 

 of full sunlight is necessary for many green aquatic 

 plants to reach maximum photosynthesis. The 

 ORSANCO committee observed that the 25-per- 

 cent level of solar radiation is not reached in many 

 of the larger streams and they considered it desira- 

 ble to restrict the addition of any substances that 



reduce light penetration and hence limit the pri- 

 mary productivity of aquatic vegetation. 



Recommendation: For effective photosynthetic pro- 

 duction of oxygen, it has been found that at least 

 10 percent of incident light is required. Therefore, 

 10 percent of the incident light should reach the bottom 

 of any desired photosynthetic zone in which adequate 

 dissolved oxygen levels are to be maintained. 



Floating materials 



Floating materials include sawdust, peelings 

 and other cannery wastes, hair and fatty materials 

 from tanneries, wood fibers, containers, scums, oil, 

 garbage, floating materials from untreated munic- 

 ipal and industrial wastes, tars and greases, and 

 precipitated chemicals. 



Wastes from paper mills, vinegar plants, cane 

 mills, and other industries may contribute nutrients 

 or produce conditions in streams that foster the 

 growth of Sphaerotilus (Chlamydobacteriales) or 

 similar iron or sulfur bacteria. These floating 

 growths not only clog fishermen's nets, but also 

 smother out the spawning grounds and habitat of 

 all forms of aquatic life. 



Recommendation: All such floating and settleable sub- 

 stances should be excluded from streams and lakes. 



Tainting substances 



Among the materials that are responsible for 

 objectionable tastes in fish are hydrocarbons, 

 phenolic compounds, sodium pentachlorophenate 

 (used for slime control in cooling towers), coal 

 tar wastes, gas wastes, sewage containing phenols, 

 coal-coking wastes, outboard motor exhaust 

 wastes, and petroleum refinery wastes. Kraft paper 

 mill wastes, sulfides, mercaptans, turpentine, 

 wastes from synthetic rubber and explosives fac- 

 tories, algae, resins and resin acids also contribute 

 to objectional tastes in fish. Twenty gallons per 

 acre of kerosene or diesel fuel will produce an off- 

 flavor in bass and bluegills which persists for 4 to 

 6 weeks. The Aquatic Life Advisory Committee 

 of ORSANCO in its Third Progress Report 

 (1960), lists the concentrations (table III-3) of 

 phenolic substances that cause taste and odor. 

 Albersmeyer and Erichsen (1959) found that car- 

 bolated oil and light oil, both dephenolated, im- 

 part a taste to fish flesh more pronounced than 

 that caused by naphthalene and methyl naphtha- 

 lene. They concluded that the hydrocarbons are 

 more responsible for tastes in fish flesh than the 

 phenolic compounds. Boetius (1954) found that 

 chlorophenol could produce unpleasant flavor in 

 fish at a concentration of only 0.0001 mg/l. 



48 



