n 



o 



o 



a. 

 z 





5S 



X 

 a 



o < 



Si 



< .1 



JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 



COLUMBIA RIVER AT ROCK ISLAND 



Average Monthly Water Quality 



1954- 1957 



FIG. 23 



52 



