The aim of this study was to determine the occurrence of caffeine in Great South bay (GSB) and to determine whether or not such detects can be used as a sewage tracer. Since caffeine is not naturally occurring its detection indicates anthropogenic input. Its value as a sewage tracer is unclear, because although its primary input is from sewage treatment plants (STPs), its input from non-point sources is unknown. Two study sites were chosen in GSB, the first was in the area of the Cedar Creek STP outfall pipe, where runoff was minimal. The second was north central GSB where sewage input is minimal, yet runoff and groundwater seepage is the major supplier of freshwater. Water samples were collected from each site, processed by solid-phase extraction (SPE), and analyzed by high performance liquid chromatography, electrospray ionization and mass spectrometry-mass spectrometry (HPLC-ESI-MS-MS). The six samples from the Cedar Creek site yielded no detectable levels of caffeine whereas the six Patchogue sites exhibited concentrations ranging from approximately 12 to 40ng/L. These concentrations are lower than concentrations observed in Boston Harbor, where caffeine has been used as a sewage tracer. This may indicate that in GSB, caffeine is not a feasible sewage tracer, as it has too many non-point sources. Simons Grant 265210 supported this study.