A study of the physicochemical and biological conditions of the Brazos River in Hood and Somervell Counties, Texas to determine the effects of a gravel dredging operation on river fauna was made in 1971-73. Physical damages resulting from dredging caused a change in the river course, depth, and substrate. Turbidity and settleable solids were increased. Alkalinity varied significantly (0.05 level) at the dredting site when gravel was taken from the river and processed. Dredging was responsible for major changes in benthic macroinvertebrate populations and fish populations in the immediate area of activity as well as in areas further downstream.