With rapid industrial development, many contaminants have been released into the environment, putting human health in risk. Black liquor is plentiful in organic and inorganic contaminants that deplete oxygen levels in water bodies and harm aquatic life. Herein, black liquor was utilized as a precursor to fabricate magnetic hydrochar using a one-step hydrothermal method. Multiple technologies were carried out to characterize the physicochemical properties of the as-prepared samples. As a result, the best magnetic hydrochar (using 1 M Fe3+) with spherical microparticles (approximately 50 - 120 nm), specific surface area (171.4 m2 g-1), total pore volume (0.146 cm3 g-1) and saturated magnetization (33.7 emu g-1) was discovered. Furthermore, its adsorption capacity was 97.40 mg g-1 and the reusability remained around 83.19 % after 5 times. The research could lead a novel, cost-effective, and environmentally friendly method of utilizing agricultural waste for aquatic environment remediation.