Molluscs are represented by snails, mussels, clams, slugs and octopuses. They evolved an advanced mode of innate immunological system which might enable them to survive and propagate for millions of years without major extinction. Multiple hemocyte-associated immunological parameters of molluscs have been reported to be immunologically sensitive to aquatic toxins of diverse nature and chemistry. Monitoring the health of aquatic ecosystems by employing a molluscan immunomarker approach has been gaining special scientific attention. Rapid contamination of aquifers by pesticides, metals, organic compounds, and nanotoxins has been posing an ecotoxicological threat. In recent years, several cellular and molecular immunological parameters of freshwater molluscs have been established as immunomarkers of toxicity of water. Hemocyte density dynamics, lysosomal dye retention, apoptosis and generation of intrahemocytic nitric oxide and superoxide anion were claimed as immunomarkers of toxicity of diverse chemical compounds. The filter feeding mode of digestion, limited mobility, prolonged life span, optimal sensitivity and resilience of immunological reactivities have been identified as advantages of molluscs to function as indicators and sources of effective immunomarkers of water pollution. In this review, the types, efficacy and prospects of potential immunomarkers of toxicity are discussed with reference to the reported freshwater molluscs. The merits of an integrative method using chemical analysis and immunomarkers for toxicity monitoring is been highlighted.