Water quality sampling, Sope Creek near Atlanta, Georgia.

Water quality sampling in a creek, Atlanta, Georgia
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Scientists from the USGS South Atlantic Water Science Center are sampling Sope Creek, Cobb County, west of Atlanta, Georgia. 

Chemical and physical consituents can vary from bank to bank even in a small creek like this. Just taking a single sample from a chosen horizontal and vertical point in the creek would not give accurate information about the water quality of the creek as a whole. Thus, samples are taken at various horizontal intervals across the creek and also in a continuous vertical column, from the surface down to the river bed. The scientist on the left is holding a churn, where all the water samples are dumped into and sufficiently mixed before a single bottle is taken (which is representative of the creek as a whole).