The diluting effect of the higher 1948 flows can more clearly be 

 demonstrated by comparing the data in terms of pounds per day rather 

 than in parts per milliono Merryfield and Wilmot did not report BOD 

 determinatiOHB during their October 1944 surveyo The 6o4 ppmo 2C-day 

 BOD reported by these authors at Wheatland during late Aiigust 1944^ 

 however, represents a demand of approximately 100,000 pounds cf 

 oxygen per day based upon river discharges at the time recorded on 

 the Salem gage twelve miles upstream. The 4o88 ppmo 20-day BOD 

 obtained at Wheatland on October 16, 1948 represents a demand of 

 approximately 250,000 pounds of oxygen per day, A similar com- 

 parison of data obtained at a common sampling point below Corvallis 

 indicates an oxygen demand of approximately 35,000 pounds per day 

 in late August 1944, in comparison with a demand of approximately 

 75,000 pounds per day in October 1948o 



The assumption appears tenable, therefore, that the pollution 

 burden of the main-stem Willamette during October 1948, was consider- 

 ably heavier than that during late August 1944, Whether the increased 

 oxygen demand stemmed from, a heavier pollution burden added to the 

 Willamette during the intervening four years or from normal seasonal 

 variations in the pollution burden cannot be determined with available 

 datae 



2e Major Tributaries 



ao Coast Fork Willamette Basin 



The changes found in both DO and BOD concentrations of water passing 

 through the Cottage Grove Reservoir presumably are not significanto The 

 sharp drop in conductivity at the downstream sampling station indicates 

 that the water being discharged from the reservoir at the time of the 

 furvey was not of the same composition as that entering the reservoiro 

 Tl'ie gradual increase in BOD and the accompanying decrease in DO' at 

 progressive stations downstream frorri the city of Cottage Grove indicate 

 the addition of oxygen-consuming was tes^-presumably domestic sewage— over 

 this areao The Cottage Grove Reservoir was being evacuated at the time 

 of the survey and the downstream reach of the Coast Fork Willamette was 

 flowing bankfull. Flows recorded at Saginaw Bridge on September 10 

 (date of survey) were 1,070 ofso in comparison with a normal seasonal 

 minimum of about 65 cfs. It is probable, therefore, that the pollution 

 added to the Coast Fork Willamette in the rieinity of Cottage Grove would 

 be serious during the period of minimum flow— as found by Merryfield and 

 Wiimoto Pollution of the Coast Fork Willamette affects only resident 

 game fishes as this tributary supports no migratorj'-fish runs. 



Neither the Row River nor Mosby Creek, major tributaries of the 

 Coast Fork Willamette, yielded any evidence of serious pollution. The 

 relatively high BOD of the Row obtained belov/ the Dorena Dam site 

 presumably resulted from temporary gravel v^ashing operatings attending 

 construction work on the dam, 



17 



