Purpose <p>The objectives of this work are to: (1) identify the difference in the performance of lanthanum carbonate-modified bentonite (LCBT), commercially available lanthanum-modified bentonite (LaBT), and iron/aluminum co-modified calcite (FeAlCA) in inhibiting the transfer of phosphorus (P) from sediment to the overlying water (OW); (2) determine the efficacy and underlying mechanisms of the combined application of LCBT and Myriophyllum aquaticum (MA) in preventing the liberation of sediment-P; and (3) evaluate the environmental safety of the combined technology based on LCBT and MA.</p> Materials and methods <p>Sediment incubation tests were conducted to (1) evaluate the ability of LCBT, LaBT, and FeAlCA to inhibit P transfer from sediment to OW, (2) to explore the effect of these materials combined with MA on P transport, transformation, and microbial communities in sediments, and (3) assess the risk of lanthanum release.</p> Results and discussion <p>LCBT exhibited good phosphate adsorption performance, with a maximum adsorption capacity of 12.4 mg g⁻¹. The lanthanum in LCBT had higher utilization efficiency for phosphate adsorption than that in LaBT. In anoxic environments, the capping treatment using LCBT was extremely efficient in suppressing the liberation of phosphorus from sediment into OW, and it showed better performance compared to LaBT. Under high-pH conditions, phosphorus immobilized by LCBT exhibited greater stability than that immobilized by FeAlCA. When the risk of P release from sediment into the pore water was high, the MA + LCBT combination effectively mitigated this risk, outperforming MA + LaBT in immobilizing the DGT (gradient diffusion in thin films)-labile P in the upper sediment layer. The MA + LCBT treatment also significantly reduced the content of mobile P, while MA + FeAlCA had a minimal impact. Following the joint treatment of MA and LCBT, sediment microorganisms retained their functionality. The risk of lanthanum release associated with MA + LCBT was far lower than that of MA + LaBT.</p> Conclusions <p>LCBT shows great promise as an active capping material for managing internal phosphorus loading. When comprehensively considering the control efficiency and long-term stability, LCBT outperforms both LaBT and FeAlCA. The MA + LCBT treatment shows great potential for addressing internal P loading, outperforming MA + LaBT and MA + FeAlCA in suppressing sediment-derived P loading when comprehensively considering the control efficiency, lanthanum release risk, and P fractionation.</p>