the simmer o This apparent anomaly stemmed in large part, no doubt, 

 from effective reaeration by biological growth which vras stimulated 

 by the organic fertilization received in the polluted reach upstream, 

 A very profuse phvtoplankton growth was apparent in the water at the 

 Athay Bridge station throughout the period of supersaturatione With 

 the exception of a single sample from the Yamhill, at no time during 

 1949 did any tributary fail to meet the accepted criteria of a re- 

 latively clean stream (ioe., a BOD of less than 3 ppm. with a DO 

 exceeding 5 ppmo) near its confluence with the main stem. Only 

 the Yamhill approached, but did not exceed, these arbitary thresholds o 



It would appear, therefore, that tributary pollution — however 

 severe it may have been diiring the summer of 1949 and irrespective 

 of its adverse effects upstream, was not a major factor contributing 

 to the main stem pollution loading. The main stem pollution problem 

 appears to be a distinct entity in itself. 



The probable magnitude of pollution abatement measures necessary 

 to eliminate the main stem oxygen block warrents considerationo At 

 the present time, two measures of pollution abatement are in progress. 



Three of the smaller impoundments of the Corps of Engineers' 

 Willamette Valley Project are in operation which have added per- 

 ceptibly to the low flows — and thus the dilution water available-- 

 in the main stem Willamette. Two major impoundments of the Project 

 currently are vinder construction and scheduled for completion within 

 four years and each of these will further increase minimum flows. 

 Fifteen additional impoundments are scheduled for construction by 

 the Corps of Engineers, plus several by the Bureau of Reclamation, 

 in the program of ultimate water development within the Willamette 

 Basin. The completed units have altered the water regimen of the 

 main stem and the major impoundments now under construction are 

 anticipated to increase minimum flows much more and, in addi+:ion, 

 reduce water temperatures to some extent as well. The completed 

 Willamette Valley Project will profoimdly affect water conditions 

 in the main stem but all effects--at least as the Project is tent- 

 atively scheduled for operation—should prove beneficial towards 

 pollution abatemento The degree to which the changes in main stem 

 conditions will improve water quality cannot be accurately fore- 

 cast with available information. 



The second corrective measure currently in progress is the 

 demand by the Oregon State Sanitary Authority that all main stem 

 communities must provide primary treatment of domestic wastes as 

 rapidly as adequate plans and financing can be secured. At the 

 present time, all wastes from these communities are discharged 

 directly into the Willamette River without treatment. As a con- 

 sequence of their action, the City of Portland is installing sewerage 

 facilities to divert all wastes to the Columbia River. The remain- 

 ing communities along the main stem have facilities for primary treat- 

 ment of their domestic wastes in various stages of planning or financ" 

 ing. The ultimate phase of the pollution abatement program of the 



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