<p>Dynamic hydro-environmental suitability maps of freshwater indicator species are useful environmental monitoring tools for tracking riverine health and informing species conservation strategies. Realized niche contraction and expansion in sympatric Asian otters represent patterns of species sensitivity to changes in riverine habitats. We employed dynamic ensemble species distribution modelling at fine spatial scales using high-resolution hydro-environmental predictors in the BIOMOD2 framework to assess the seasonal hydro-environmental suitability of the smooth-coated otter (<i>Lutrogale perspicillata</i>, SCO) and Asian small-clawed otter (<i>Aonyx cinereus</i>, SCL) in the Bhavani-Noyyal river basin of the southern Western Ghats. SCL suitability increased during wet seasons along lower-order streams. SCO favoured wider rivers and backwaters and higher river ratio, showing greater seasonal stability. Streams inside the reserve consistently supported higher environmental suitability for both species; however, for SCO some suitable habitat patches were predicted outside the reserve. Hydromorphological gradients were the primary drivers of suitability for both species, while seasonal changes in water quality mainly total dissolved solids, ammonia, and dissolved oxygen were secondary, reach-scale regulators. Niche overlap was lowest in the first dry season and progressively increased in the wet season as SCL niche expanded into SCO occupied areas at river confluences. Seasonal variation in water quality and hydromorphology appear to shape the Grinnellian niche of sympatric otters at local scales. Hydrological connectivity and hydro-environmental conditions are critical for the conservation of sympatric otters in the Western Ghats. The patchiness of optimal habitats and pronounced seasonal shifts highlight the need for seasonally adaptive riverscape management under future environmental change.</p>