This report presents the results of a study by the U.S. Geological Survey, in cooperation with the City of Columbus, Ohio, to determine the distribution and variability of fecal-indicator bacteria in Scioto and Olentangy Rivers. Fecal-indicator bacteria are among the contaminants of concern to recreational users of these rivers in the Columbus area. Samples were collected to be analyzed for fecal-coliform and Escherichia coli (E. coli) bacteria and selected water-quality constituents and physical properties at 10 sites-- 4 on the Olentangy River and 6 on the Scioto River during the recreational seasons in 1987, 1988, and 1989. Measurements of streamflow also were made at these sites at various frequencies during base flow and runoff. The concentrations of fecal-coliform and E. coli bacteria in the Scioto and Olentangy Rivers spanned a range of five orders of magnitude, from less than 20 to greater than 2,000,000 col/100 mL (colonies per 100 milliliters). In addition, the concentrations of fecal coliform and E. coli bacteria are well correlated (r=0.97) in the study area. At times, relatively high concentrations, for fecal-indicator bacteria (concentrations greater than 51,000 col/100 mL for fecal-coliform and E. coli ) were found in Olentangy River at Woody Hayes Drive and at Goodale Street, and in Scioto River at Greenlawn Avenue and at Columbus. Intermediate concentrations of fecal-indicator bacteria (from 5,100 to 50,000 col/100 mL for fecal coliform and (from 510 to 50,000 col/100 mL for E. coli ) were found in Scioto River at Town Street and below O'Shaughnessy Dam near Dublin, Ohio, and in Olentangy River at Henderson Road. The lowest (median) concentrations of fecal-indicator bacteria (from 20 to 5,000 col/100 mL for fecal coliform and from 20 to 500 col/100 mL for E. coli ) were found at Olentangy River near Worthington, Ohio, Scioto River at Dublin Road Water Treatment Plant and below Griggs Reservoir. Fecal-coliform concentrations exceeded the geometric mean and single-sample Ohio Water Quality Standards for recreation less frequently than E. coli concentrations. The E. coli numerical water-quality standards are more difficult to meet than the fecal coliform standards because they are as much as an order of magnitude lower in some instances. The geometric mean bathing-water and primary-contact standards for fecal-coliform and E. coli bacteria were exceeded in more samples for Olentangy River at Goodale Street than for any other site. The single-sample bathing-water standard for fecal-coliform bacteria was exceeded in 83 percent of all samples and for E. coli in 91 percent of samples for Olentangy River at Goodale Street. Compared to Olentangy River at Goodale Street, geometric means and single-samples exceeded the bathing-water standards somewhat less frequently for Scioto River at Town Street and far less frequently for Scioto River at Dublin Road Water Treatment Plant. In contrast to results for fecal-indicator bacteria, the differences between sites for pH and for concentrations for total alkalinity, total chloride, total nonfilterable residue, total nitrate plus nitrite as nitrogen, total phosphorus, and total organic carbon were small. The large contribution of streamflow and discharge of fecal-indicator bacteria from Olentangy River to Scioto River has a major effect on the Scioto River downstream from the confluence of Olentangy River during periods of rainfall and runoff. Fecal-indicator discharges were calculated for times before, during, and at 24-hour intervals for 48 to 72 hours after two runoff-producing storms. Fecal-coliform and E. coli concentrations were lower in samples collected before runoff and during receding streamflows at 24- to 48-hours after the storms than in samples collected during runoff. The fecal-indicator discharges entering Scioto River from Olentangy River ranged from 22.6 to nearly 100 percent of the total for two storms studied. Controlling nonpoint, unregulated,