Eastern oysters (Crassostrea virginica) were sampled at 6 sites along the length of Calico Creek, a sewage effluent impacted tidal creek in Morehead City, North Carolina, USA on a biweekly basis during June and July, 2009. Potential impact of sewage effluent on oysters was tested by assaying phenoloxidase activity and alkali-labile phosphates, as well as by measuring condition index, and histological analysis of gonadal tissue. The study found no significant differences between the sites for phenoloxidase activity, alkali-labile phosphate levels, or condition index. All three parameters shifted during the summer however, suggesting the possibility of endocrine disruption. The sites closest to the effluent input demonstrated more mature gonads, significantly larger eggs (p< 0.05), and a larger proportion of males, although it was unclear if these results were caused by nutrient loading or endocrine stimulation.