Daily observations of water temperature for 20 sites in the lower Columbia River are presented in tabular form and in profile form by months for the period August 1941 to July 1942. The profiles show minimum, mean (average), and maximum water temperatures for those months from river mile 142 to river mile 6.7. The data indicate that water temperature in the lower river trends upward from October to March and has no marked trend, or trends downward, during April to September.
Analysis of the water-temperature records at Bonneville Dam (river mile 146.1) for the 1938-66 period of record show-s that the months from August 1941 to July 1942 are fairly representative of average conditions except for August and January, which are about 3 ?F above and 4 ?F below average, respectively. Analysis of the Bonneville Dam records also indicates that in the mid-1950's a man-caused change in water-temperature regimen occurred that resulted in higher temperatures at Bonneville Dam for 10 months of the year but no change in March and April. The changes for the other months ranged from +0.5 ? to +2.0?F. This means that average temperatures for the lower river are now somewhat warmer for most months than temperatures shown in the profiles.