[en] Formation of THMs (CHCl_3, CHCl_2Br, CHClBr_2 and CHBr_3) due to chlorination of cooling water though unintended is unavoidable. Discharge of these chlorination byproducts (CBPs) into the sea is a concern over its toxicity to the marine organism and consequently to human through food chain process. In view of this, formation of trihalomethanes in the cooling seawater discharge of MAPS, Kalpakkam, India was investigated. Chlorination experiments were carried to evaluate the expected THMs load in the discharge water during different operational scenario. Effect of temperature (20 °C, 30 °C and 40 °C), chlorine dose (1, 3, 5, 10 ppm) and contact time (0.08-168 hrs) on the formation characteristics of THMs was studied for seawater. Instantaneous oxidation of seawater bromide to Br_2 by Cl_2 (K_2_9_8 = 2.95*10"-"3 sec"-"1) ensued the former to be dominant participatory oxidant species which affected the distribution and load of CBPs. Bromoform was the single largest THM comprising more than 95% of total THMs formed under all investigated chlorination conditions. As expected, THM load increased, however, halogen incorporation ratio decreased from 12 % (for 1ppm Cl_2) to 5% (for 10 ppm Cl_2). Temperature coefficient was determined for THMs formation for chlorine dose ranging from 1-10 ppm. Formation of small amount of CHCl_2Br and CHClBr_2 were noticed at higher temperature with high chlorine dose after a long contact time. Periodical monitoring of MAPS cooling seawater discharge during the last four year revealed THMs content varied between BDL- 51μg/l which was mostly comprised of CHBr_3 and CHCl_3, CHCl_2Br and CHClBr_2 were remained undetected most of the time. (author)