The Public Health Service initiated a study to determine the need for and value of storage in Senator Wash Reservoir for regulation of streamflow and water quality control. The report includes the results of a study on general public health and vector control aspects of the project. Salinity is a serious problem in the Colorado River below the confluence of the Gila River. Bacteriological densities, in excess of desirable limits, are caused by discharge of raw sewage from Yuma, Arizona. Storage of water in the Senator Wash Project for mineral quality control is not recommended until salt discharges have been controlled. Reduction of flows in the Colorado River would also increase the problems associated with sludge discharge.