The use of cerium dioxide manufactured nanoparticles (CeO2 MNPs) at a large scale in the industry, automotive and everyday products is resulting in a continuous emission and release of CeO2 MNPs to the aquatic environments. In such complex systems, MNPs interact with water components, including biopolymers, resulting in MNP coating which give a new environmental identity to the MNPs and greatly influence their fate, transport and biological impact. MNP surface properties, aggregation, media composition such as ionic composition and pH, strongly influence the importance of natural organic matter coating and coating stability with time. In our study, we are using alginate, a relevant surrogate of natural organic polysaccharides, to coat CeO2 MNPs under different conditions from ultrapure water to synthetic and natural waters. First, the most favourable conditions of alginate coating are defined and then the stability of this coating in changing pH condition is investigated. Then alginate coating impact, at variable alginate concentration, is studied in synthetic and natural waters and comparison is made with ultrapure water. The possible interaction mechanisms between alginate, CeO2, dissolved ions (in particular divalent cations) and natural inorganic compounds are discussed. Our finding demonstrates that alginate concentration, solution pH and presence of divalent cations are key parameters defining the stability and effect of alginate coating and that once formed the biopolymer coating is found irreversible with time and when changing the solution chemistry.