Biological Survey — Genesee River 35 



converts the stream into a long, sluggish pond, lined with vegeta- 

 tion. At the time investigated the contamination was probably 

 close to its maximum, and the content of dissolved oxygen showed 

 a steady decline along the course of the stream, reaching a mini- 

 mum of 3.9 per cent of saturation at the dam. This and the 

 accompanying rise of carbon dioxide are illustrated in Figure 7. 



(3n a day other than when these chemical determinations were 

 made minnows and other species of fish did not long survive 

 when placed in the water about three-quarters of a mile below the 

 entrance of pollution.* 



Ai)art from streams, a brief investigation was conducted upon 

 the waters of Silver lake. This lake is peculiar in that both inlet 

 and outlet are at the same end and but a short distance apart. 

 As a result the water is more or less stagnant, and at the time of 

 investigation was exuberantly supplied with plankton growtli. 

 Samples were taken at regular intervals from top to bottom, and 

 analysis showed a progressive diminution in dissolved oxygen, 

 agreeable witli the expectation of decomposing plankton. 

 (Fig. 8.) 



Summary. — To assist in interpreting the tabulated data, a 

 brief summary of conclusions follows : 



The pollution of Cryder creek at Whitesville was considerable 

 and marked by a heavy fungus growth. At a point about 4,000 feet 

 below, improvement was noted and corresponded with the return 

 of the less tolerant organisms, but recovery was not complete, 

 and the stream was found to enter the river bearing a cargo of but 

 partially assimilated ])ollution. 



Apart from a seepage of oil from wells and tanks which filmed 

 its surface along the upper part of its course, Brimer brook 

 received the effluent from a cheese factory at Petrolia, evidence 

 of which was appreciable for half a mile below, but recovery 

 ])ractically complete one mile from source of pollution. 



Pollution of Chenunda creek by a cheese factory effluent at Hall- 

 l)ort was slight and dependent u])on weather conditions, inasmuch 

 as a srnall stream which received the waste directly seeped into 

 the earth during dry seasons. 



Black creek, polluted by cheese wastes at Birdsall, was unsatis- 

 factory from the standpoint of volume until supplemented by 

 tributary waters more than a mile below, and here recovery was 

 almost complete. 



Investigation of Caneadea creek showed that the tributary 

 stream which under other conditions would have received cheese 

 wastes at West Branch was dry. Similar ])ollution at Hardy 



* From notes supplied by Emmeline jNIoore the fish used in the test were: 

 4 blunt-nosed minnows (2%-2% in.); 1 yellow peroh (-Zy^ in.); 2 common 

 shiners (3% and 4% in.); and 3 common* suckers (4,^.-4% in.). They suc- 

 cumbed in the followintj^ order: Blunt-nosed minnows and perch (in 12 min.) ; 

 common shiners (in 15 and 16 min.); suckers (in 24, 33' and SSy^ min.). 

 Tlie time was late afternoon, Aug. 31, 1U26; air temperature, 67°~ Fahr.; 

 water temperature, 74° Fahr. 



