An ox^'gen block appeared in early summer at 

 the upper end of the reservoir in 1962. No distinct 

 block was recorded in 1063, but some oxygen de- 

 pletion was detected in the same areas. 



Changes in temperature and oxygen concenti'ii- 

 tions were significant during 24-hour sampling 

 periods in July and August. These changes could 

 have influenced diunaal vertical movements of sal- 

 monids. Diurnal changes in temperature and oxy- 

 gen concentrations were not significant during 

 spring and fall. 



Carbon dioxide, silicates, sulfates, hydrogen-ion 

 concentration, conductivity, alkalinity, and turbid- 

 ity were within acceptable limits for fish life, al- 

 though hydrogen-ion concentrations and conduc- 

 tivity reached nearly critical values at times. 



Continuous recordings of surface currents in 

 1964 indicated that downsti-eam orientation of cur- 

 rents and current velocity changed significantly 

 during five reservoir stages: (1) maximum draw- 

 down, (2) minus 13.4-m. level with high inflow 

 and outflow, (?>) fill-up without spill, (4) full pool 

 with heavy spill, and (Ti) full pool without spill. 

 The conditions of currents for downstream move- 

 ment of salmonids were best during maximum 

 drawdown and at the minus 13.4-m. level with high 

 inflow and outflow. 



Instantaneous measures of current velocity and 

 direction indicated that current velocities increased 

 throughout the reservoir at a maximum drawdown 

 of 27.1 m. ; measurable velocities were detected at 

 most depths from the upper to the lower end of 

 the reservoir. Velocities decreased and current di- 

 rections became erratic during fill-up. Significant 

 spills at the dam increased currents and changed 

 direction of the flow in the upper levels throughout 

 most of the iTservoir during April and June 1964. 



"Wind velocities influenced surface currents in 

 the lower and middle reservoir. The effect of wind 

 was strongest at midreservoir, where current ve- 

 locities were lowest. A strong wind of 32 km.p.h. or 

 more could reverse the direction of the surface 

 current at all sections of the reservoir. 



Brownlee Reservoir significantly aft'ected the 

 temperatures and oxygen concentrations of the 

 Snake River below tlie reservoir. Temperatures 

 below Brownlee Dam were about 5° C. higher 

 than temperatures in the ri\er above the reservoir 

 during October. C^onvcrsely, oxygen concentrations 



l>elow the dam were 5 p. p.m. lower than in the 

 inflow. These conditions were reversed in June and 

 July. In general, the reservoir had a Inift'ering ef- 

 fect on temperatures, oxj'gen concentrations, and 

 alkalinity. 



The main conclusions bearing on movements of 

 salmon were : 



1. Temperatures, oxygen concentrations, and 

 currents are the most critical of the enviromnental 

 factors that can affect the distribution and sur- 

 vival of salmon in Brownlee Reser\'oir. 



2. Environmental conditions for salmon at 

 Brownlee Reservoir are suitable, if not optimal, in 

 the spring, late fall, and winter. Growth, move- 

 ment, and survival of resident juvenile salmon dur- 

 ing the late summer and early fall can be seriously 

 restricted. 



•'i. Diurnal physical and chemical changes are 

 not sufficient to cause any radical change in the 

 l>ehavior of salmon during the spring and fall. 

 Diurnal variations in the summer, however, can 

 significantly influence vertical movements of 

 salmon within a 24-hour cycle. 



4. Surface and subsurface currents are signifi- 

 cantly affected by changes in reservoir level and 

 volumes of inflow and outflow. These changes can 

 influence success in passage of juvenile salmon. 



5. Brownlee Reservoir alters the water quality 

 of the Snake River below the dam in the spring and 

 fall. These changes are of particular importance to 

 adult fall-nm salmon migrants beca.use the reser- 

 voir at this time not only delays the cooling cycle 

 of tlie river but also lowers the oxygen content to 

 nearly critical levels for salmon. 



ACKNOWLEDGMENTS 



John R. Donaldson, Oregon State ITniversity, 

 critically reviewed this paper. The U.S. Depart- 

 ment of the Interior Geological Survey and Idaho 

 Power Company provided data on Snake River 

 flows. Donald Montgomery, project leader of this 

 study in 1962, provided the data for that year. 



LITERATURE CITED 



American Pitblic Health Association. 



1960. Staiulara methods for the examination of 

 water and wastewater including bottom sediments 

 and sludges. Amer. Public Health Ass., Inc.. New 

 York, 626 pp. 



334 



U.S. FISH AND WILDLIFE SERVICE 



