STREAM POLLUTION 
395 
suspensoid particles as they lodge on the gills and other exposed parts. Conse- 
quently, healthy and uninjured fishes can move through very muddy water or water 
carrying considerable quantities of pulps (Cole, 1935b), sawdust, and other suspensoids 
and receive little or no mechanical injury to the gills. However, as has been pointed 
out by Marsson (1911), small amounts of various acids, chemical wastes, and other 
substances which in themselves either injure the gills or alter the flow of mucus 
may greatly augment the mechanical action of the suspensoids, with serious results 
to the fish, so that through the combined action of these chemical agents and the 
suspensoids the abrasive action on the gills may be increased or the gills matted with 
deposits which under more favorable conditions would have been washed away by the 
mucus. 
Indirectly, but none the less effectively, erosion silt affects fisheries by screening 
out the light, by “laking down” organic wastes, and thus increasing the oxygen de- 
mand at the bottom of the stream, and by retaining many forms of industrial effluents 
as oils, chemical wastes, and pulps in beds on the floor of the stream, with disastrous 
results to the bottom fauna. 
Summarized data on turbidity of and light penetration into various stream 
waters are presented in table 3. 
Table 3. — Turbidity of stream waters as measured by light -penetration ( millionth intensity depth in 
meters) in various river systems during June to September, inclusive, 1932-35 
[For convenience of comparison, data are expressed as percents of the total number of determinations for each stream unit] 
I 
Light penetration expressed as millionth intensity depth 
in meters 
River system 
Composite, streams supporting good mixed fish 
fauna 1 
Mississippi, flowing streams, good fish fauna 
Mississippi, flowing streams, medium, poor, or no 
fish fauna 
Mississippi, impounded water, Hastings Pool 
(Minn.) 
Mississippi, impounded water, Lake Pepin (Minn.- 
Wis.)_ - 
Mississippi, impounded water, Lake Davenport and 
Moline Pool (Iowa-Ill.) 
Mississippi, impounded water, Lake Keokuk 
(Iowa-Ill.) 
Missouri, headwaters, clear streams (Mont.-Wyo.)_. 
Missouri, below headwaters (Mont., Wyo., Colo., 
Nebr., Kans., Mo.) 
Ohio (Pa., W. Va„ Ohio, Ky., Ind., 111.) 
Tennessee, flowing streams (Ky., Tenn., Miss., 
Al3.)__ 
Atlantic-coast streams (Maine to S. C., inclusive) 
Gulf-coast streams (Fla. to Tex.) 
Rio Grande, flowing streams (Tex., N. Mex., Ariz.)._ 
Colorado, flowing streams (Ariz.-Nev.) 
Columbia, flowing streams (Idaho, Mont., Wash., 
British Columbia) 
Num- 
ber of 
sta- 
tions 
Num- 
ber of 
deter- 
mina- 
tions 
Clear 
Cloudy 
Turbid 
Very 
turbid 
Muddy 
Very 
muddy 
5.00- oo 
4.90- 
1.00 
0.99- 
0.50 
0.49- 
0-30 
0-29-0-15 
0.14-0 
202 
514 
35 
24 
17 
9 
9 
6 
52 
237 
4 
11 
8 
16 
25 
36 
79 
260 
1 
18 
11 
14 
38 
18 
1 
17 
100 
12 
73 
11 
88 
1 
13 
175 
51 
19 
19 
4 
7 
16 
571 
19 
28 
20 
16 
17 
5 
15 
20 
60 
20 
19 
23 
44 
31 
4 
4 
17 
41 
82 
12 
5 
15 
7 
48 
13 
93 
158 
11 
8 
32 
32 
17 
11 
16 
36 
37 
18 
9 
11 
in 
18 
46 
18 
18 
6 
25 
88 
4 
8 
7 
36 
67 
22 
8 
3 
3 
17 
31 
49 
39 
3 
3 
3 
Grand totals: Stations, 585; light-penetrat.ion determinations, 2,344 
1 Derived from light-penetration determinations made at 202 stations in the Mississippi, Missouri, Tennessee, Atlantic coast* 
Gulf coast, Rio Grande, Colorado, and Columbia systems, at each of which stations good mixed flish faunae and associated organ- 
isms were thriving. Each of these 8 stream units are given equal value in the expression of the composite. 
99773° — 37 5 
