The surface water parameters such as temperature, salinity, conductivity, dissolved oxygen, pH and turbidity of Port Blair bay, Andaman & Nicobar Islands were measured in situ over 104 sampling points using a digital multi-parameter water quality instrument and a Global Positioning System (GPS) during high tide. These parameters were subsequently interpolated over the entire bay using three methods, viz., Inverse Distance Weighted (IDW), Spline and Kriging. The interpolated values over the sampling points were compared with the corresponding measured values by means of three statistical indices: Mean Absolute Error (MAE), Root Mean Square Error (RMSE) and Index of Agreement (d). It was found that among the three interpolation methods, IDW method showed better matching between the measured and interpolated values for four out of six parameters whereas Kriging method showed better results for the remaining two parameters with lower MAE and RMSE values, and higher values of 'd'. This paper describes the details of interpolation methods and its suitability to assess water quality parameters in the bay. In addition, it also highlights the capability of GIS as a tool to model spatial changes in environmental systems.