Nitrogen discharged into lake ecosystems typically has different nitrogen stable isotope ratios(δ¹⁵N) and measurement of δ¹⁵N in organisms can be useful indicators of anthropogenic impacts from the watershed. The δ¹⁵N values of Bellamya aeruginosa were investigated in four bays of Lake Taihu. Results showed that δ¹⁵N values in snail ranged from 6.9‰ to 18.1‰, with an average of 11.2‰. Snail δ¹⁵N values displayed a significant variation among four bays. The highest average value was found in Meiliang Bay(17.7‰), followed by Gonghu Bay(13.2‰), East Taihu(10.2‰) and Zhushan Bay(7.8‰). Our investigation suggested that both Meiliang Bay and Gonghu Bay have received tremendous amount of domestic sewage derived from increasing human activities. Therefore, it's necessary to promote investment of sewage treatment plants in surrounding cities including Wuxi and Changzhou. Our research also indicated that Zhushan Bay, which is located in northwest part of Lake Taihu is mainly affected by agriculture non-point source pollution. So it's necessary to reduce the use of fertilizers to improve the water quality of that bay.