A study was conducted on the riverine health of the lower reaches (approximately 36.10 km in length) of the transboundary river Lohit, which spans approximately 460 km within Arunachal Pradesh, India, for two years, from 2020 to 2022. The observations recorded seasonal variations in its physicochemical profile, and macroinvertebrates richness, which serves as a bioindicator. A total of 22 physicochemical parameters were examined and grouped into two categories for the convenience of statistical analysis. These parameters displayed seasonal fluctuations but remained within the optimal range. It also recorded richness of macroinvertebrates falling under the phyla Arthropoda and Mollusca, revealed 13 orders, 35 families, and 38 species. The statistical analysis of correlation and Principal Component Analysis of macro invertebrates, with observed physiochemical parameter elucidate the strong complex inter-relationships. It highlighted a multifaceted pattern in the variables characterized by opposing influences. The Heat map documented a uniform distribution of parameters and macroinvertebrates except in Ephemeroptera and Trichoptera in all four sampling sites throughout the study period. The study shows a complex but stable ecosystem during the study.