Coliforms and microplastic pollution are major issues prevailing in the estuarine ecosystem. At present, the Adyar river in Chennai, Tamil Nadu is under threat due to sewage disposal and solid waste dumping. In the present investigation surface water samples were collected from five sampling locations and analyzed for coliforms, microplastics (MPs), and the development of biofilm. The maximum coliform population of 75±6-228±12 MPN/100mL was observed during the pre-monsoon period. The MP content was in the range of 90-230 particles /L, 70-210 particles/L, and 90-190 particles/L for pre-monsoon, post-monsoon, and summer seasons respectively. The development of black crystalline colonies on Congo Red Agar (CRA) medium explained the occurrence of biofilm in the study area. Further, biofilm formation was higher during summer when compared with that of pre-monsoon and post-monsoon seasons. The plastic particles collected from the sampling locations were having rough surfaces. More bacterial colonies were observed on polyethylene (PE) MPs when compared with that of polyamide (PA) and Nylon under laboratory conditions.