<p>Understanding the mechanism and storage of phosphorus (P) in riverbed sediment is a prerequisite for better management and protection of water resources, ensuring a sustainable ecosystem and safe water for human use. This study describes the adsorption behaviour of P in sediment collected from the Ganga and Yamuna rivers at Prayagraj, India, employing both kinetics and isotherm models. The sediment showed significant physicochemical characteristics, with Ganga characterized by high sand (91.76%) content and low organic carbon (OC) content (0.14%), while Yamuna exhibited high clay (37.33%) and OC (0.62%), indicating more reactive surfaces. The results demonstrated that at equilibrium, P adsorption was 89% in Yamuna sediment and 23% in Ganga sediment. Among kinetic models, the pseudo-second order (PSO) model best described P adsorption for both rivers, with high <i>R</i>² values (0.96 for Ganga, 0.99 for Yamuna) and acceptable RMSE and <i>χ</i>² statistics, indicating a chemisorption-dominated mechanism. The intraparticle diffusion (IPD) model further suggested that pore diffusion also played a role and was more dominant in Ganga sediment (<i>R</i>² 0.90) as compared to Yamuna sediment (<i>R</i>² 0.74). Qe_model had a better agreement with Qe_calculated for the PSO in both sediments. Among isotherm models, the Langmuir model exhibited an excellent fit to the adsorption data for Ganga sediment (<i>R</i>² 0.95), indicating monolayer adsorption on a relatively homogenous surface, while the Temkin model described the adsorption data best for Yamuna sediment (<i>R</i>² 0.97), suggesting a combination of physical and chemical adsorption on a heterogeneous surface. These findings highlight the critical influence of sediment texture and OC content on P adsorption dynamics, with the Yamuna sediment showing superior adsorption potential due to its finer texture, higher OC, clay content, and Fe/Al oxides contents. The models studied may be useful for P risk assessment in aquatic environments.</p>