Levels of bacteria in excess of water quality standards for contact recreational designated use have been documented in Gilleland Creek, located in northeast Travis County, Texas. Stormwater monitoring showed increased bacteria levels after rainfall runoff events in Gilleland Creek, and analysis indicates the bacteria is of a nonpoint source origin. The objective of this research was to modify a flood control basin in an urban area in the upper part of the Gilleland Creek watershed to determine whether it is possible to substantially increase bacteria removal by retaining stormwater in the basin for 24 hours after a storm event. Bacteria reduction was predicted as a result of sedimentation and exposure to sunlight. The outlet of one flood control basin was retrofitted with an automated gate valve to control stormwater outflow and acted as the test basin. Another flood control basin, located approximately ¼ mile from the test basin, was unmodified and acted as the control basin. Stormwater monitoring at the inlet and outlet to both basins over the course of five storm events showed that neither the control nor the test basin exhibited a decrease in E. coli concentrations. Both basins were effective in decreasing the concentration of total suspended solids and showed varying performance for the treatment of nutrients. The dataset is limited by the small number of storm events that were sampled, and continued stormwater monitoring would offer additional insight into retrofit performance. / text