Anthropogenic habitat transformations involving changes in hydrologic conditions in the peatlands of eastern Poland contribute to the disappearance of sites of numerous relict plant species. The study aimed to verify whether sites chosen for the reintroduction of the endangered species Salix lapponum had been well selected by analyzing selected habitat parameters and determining whether changes in their values may in the long term have a significant impact on the functioning of new populations of the species. The results obtained at sites where the S. lapponum population was replenished with new individuals were analyzed in relation to data from one of the natural sites of the species. Hydrochemical characterization of the groundwater at the study sites confirmed that there was no significant influx of nutrients into the habitat or other hydrological disturbances due to human activity. The values obtained for the factors tested were within the limits of the specific preferences of the species. Changes in the values of some physical-chemical parameters of the water were due to the ecosystem’s internal metabolism, and the site with the highest hydrochemical stability was the one where S. lapponum occurred naturally. The species composition and structure of the phytocoenoses at all study sites were characteristic of natural sites of the species and showed no disturbances caused by human impact. The microbiological analyses indicated normal soil processes. The hydrochemical and biocoenotic stability of the habitat, including the microbiological balance of the soil, which was free of pathogenic fungi, should have a positive effect on the condition of the reintroduced plants.