<p>Hydraulic conductivity governs seepage, drainage, and long-term soil performance, and conventional stabilisation methods often carry high environmental costs. Biopolymers have emerged as sustainable alternatives capable of modifying soil behaviour through hydrogel formation, pore filling, and viscosity-induced flow resistance. This review synthesizes current findings on biopolymer-treated soils, demonstrating that biopolymers effectively reduce permeability, particularly in coarse-grained soils where initial hydraulic conductivity is high, while enhanced reductions in fine-grained soils are attributed to strong polymer–particle interactions. Treatment efficiency is strongly influenced by soil type, fines content, dosage, curing conditions, and pore-fluid chemistry. Emerging evidence also highlights key long-term considerations. Biopolymer-treated soils exhibit encouraging durability under limited wetting–drying cycles, yet long-term stability remains uncertain due to biodegradability and chemical sensitivity. Research on cyclic hydraulic, thermal, or chemical loading is sparse, and field-scale validation remains largely unexplored. Overall, biopolymers provide a promising, environmentally responsible approach to soil stabilisation. Future work should prioritise long-term durability, biodegradation mechanisms, cyclic loading behaviour, and full-scale field studies to establish reliable design guidelines for sustainable ground-improvement applications.</p> Graphical abstract <p></p>