Environmental pollution is currently a major concern due to unorganised and increased industrialization and urban development. In the Tamilnadu state of India, on the Bay of Bengal, lies the Ennore estuary, which is an important industrial centre. The main industries in the region include a fertilizer company, refineries, a rubber factory, paint industry and a thermal power station. Investigations into the seasonal pollution impacts on the distribution of various metals in the waters of the Ennore estuary, situated in North Chennai, Tamilnadu, India, and the concentrations of some of the toxic metals in the tissue of the grey mullet, Mugil cephalus L., inhabiting in the same estuary were conducted during the period of April 2004 to March 2006. The results were compared to those of the Kovalam estuary, which is unpolluted. In the water at one sample site of the Ennore estuary, heavy metal concentrations ranged between: Pb 0.15-0.23, Hg 0.05-0.06, Cd 0.01-0.03, and Cr 3.33-1.093 ppm for summer and monsoon seasons, and were significantly related to the seasonal rains (p<0.01). In contrast, heavy metal concentrations in the Kovalam estuary ranged between: Pb 0.043-0.039, Hg non-detectable-0.001, Cd 0.01-0.098, and Cr 0.063-0.052 ppm, and were not significantly related to the rainy season. The metal concentrations found in the muscle tissues of Mugil cephalus L., at the same site on the Ennore estuary were: Fe 11.06 ±0.29, Zn 1.67 ±0.14, Cr 2.98 ±0.15, and Pb 1.26 ±0.11 ppm, which were also significantly related to season (p<0.01). The metal concentrations in fish inhabiting the Kovalam estuary were: Fe 2.17 ±0.15, Zn 0.42 ±0.05, Cr 0.63 ±0.04, and Pb 0.31 ±0.04, and showed no significant seasonal difference. The highest metal concentrations found in the tissues of the Ennore estuary fish which lead to the oxidative stress and shorten the lifespan of the fish are postulated to primarily result from anthropogenic activities and effluent discharge from the local industrial activities.