Tolly''s Nullah is fed with fresh water during flood- tidal flush of the Hooghly (Ganga) River. Tolly''s Nullah, running through the southern part of Kolkata metropolis is subjected to the influx of effluents from domestic sewage and rainwater run-off. This effluent load makes stupendous change in the ecosystem and ecological behavior of the water body. The water quality is tested by drawing samples from six strategic locations under different climatic conditions as well as under flow and ebb tide conditions. Standard testing methods have been adopted for the measurement of water quality parameters. The present work is an attempt to understand the water quality based on the estimation of physico-chemical parameters of the surface water using DELPHI, CCME Water Quality Index and Statistical analysis methods.