Freshwater ecosystems and associated habitats harbor incrediblebiodiversity. They offer various ecosystem services andsustain human livelihoods. However, due to increasing developmentalpressure and rising water demand, these systemsare under huge threat. As a result, many aquatic species arefeared to become extinct in near future. Quantifying the patternsof aquatic species diversity and composition of river systemsis urgently required. With this interest, we studied fourriver systems in the Western Ghats region, documenting thepattern of fish diversity and identifying the factors that influencefish species richness. Maintaining undisturbed streamsand river basins, especially headwater regions is crucial forsustaining freshwater biodiversity in the tropical river ecosystems.