The applications of TRIX-based indices are more effective methods to understand the source, transport of contamination and its effect on the ecosystem. In the present study, the changes to the trophic status of Pulicat lagoon over a decadal scale using multiple annual and seasonal datasets for the years 2005-2006, 2006-2007, and 2016-2017 has been carried out to understand the application of TRIX in the aquatic ecosystem. We derived TRIX-based indices using the globally recognised Vollenweider’s indexing methodology for the lagoon, for which previously classical indices using Carlson’s Trophic State methods had been derived. Using the new methodology to understand the trophic status, we illustrate the eutrophic status of the whole lagoon ecosystem, comparing the decadal datasets represented by a spatial interpolation model. Further, we combined the US EPA-based ASSETS model results to confirm the trophic status given lagoon-specific parameters over a decadal scale. The study provides data on the trophic conditions of the ecosystem, confirming the increasing eutrophic status over the past decade and providing significant information to the coastal managers for further action.