Abstract  This paper summarizes over four years of studies and testing of a sinkhole/spring system in north Tampa. Sulphur Springs Pool delivers an average of 95 million l/d to the Hillsborough River, which is tributary to Tampa Bay. In 1986, owing to increasingly erratic bacterial levels at the natural bathing area adjacent to Sulphur Springs, the Hillsborough County Health Department closed the pool for swimming. The City of Tampa, Southwest Florida Water Management District (SWFWMD), Hillsborough County Environmental Protection Commission, and the United States Geological Survey have gathered data in an attempt to better understand the system and possible sources of contamination. The Sulphur Springs Action League is a civic group in the area, which has an objective of reopening the pool for recreational purposes. Environmental Engineering Consultants, Inc. provided pro bono technical assistance and expertise in assisting the Action League with its goal. The Action League obtained a grant from SWFWMD to outfit underwater divers for sinkhole exploration as well as water quality and dye trace analysis. The main suspects for bacterial contamination of the pool were two significant sinkholes located 1950 and 2300 m north of the spring. A series of dye tests and water-quality tests were performed. It was estimated that the underground velocity of water was between 90–100 m/h. Using a dye trace, bacteria testing, and travel time estimating, a new source of contamination was found in a Department of Transportation (DOT) stormwater retention basin in which a sinkhole had opened up and was receiving stormwater. The two significant sinkholes received stormwater from commercial and residential areas, and this stormwater brings a large amount of bacteria into the sinkhole, which funnels into the underground system and induces a bacteria spike at Sulphur Springs pool that exceeds the bathing water standards. The City of Tampa has constructed an experimental initial flush capture basin that will sand-filter stormwater to see if this will favorably affect bacteria levels. A mayor''s task force in Tampa has recommended ultraviolet disinfection as an interim solution to the contamination problem.