Water samples collected from 40 stream sites in the Ohio River Watershed in Indiana from May through August 2000 were analyzed for concentrations of Escherichia coli (E. coli) bacteria. Each site was sampled five times in a 30-day period. Concentrations of E. coli in 72 of the 200 samples exceeded the State of Indiana single-sample standard of 235 colonies per 100 milliliters for waters used for recreation.
A five-sample geometric mean of concentrations was computed for each site. Concentrations in samples from 24 of the 40 sites exceeded the State of Indiana standard for a five-sample geometric mean of 125 colonies per 100 milliliters for waters used for recreation. Samples collected from 34 sites had E. coli concentrations that exceeded either or both the single-sample standard and the five-sample geometric mean standard.
Five of the 40 sampling sites were at or near U.S. Geological Survey streamflowgaging stations. On the basis of records from these stations, 16 percent of the samples from these sites were collected at streamflows above the median daily mean discharge for each station.
E. coli concentrations and turbidity measurements collected during 2000 were analyzed in concert with E. coli concentration and turbidity data collected in 1999 at streams within the Kankakee and Lower Wabash River Watersheds in Indiana and in 1998 at streams within the Upper Wabash River Watershed in Indiana. These data were grouped together to investigate the relation between concentrations of bacteria and turbidity. The resulting analysis indicated a statistically significant correlation between concentrations of E. coli and turbidity.
