In the article a role of the flow bog in the transformation of the physical-chemical properties of waters was described. They demonstrated that in the water flowing out of the bog a fall in the mineralization and concentrations of selected ions take place towards feedwaters. The species stated within the bog of plants, mainly Carex rostrata, Schoenoplectus lacustris, Equisetum fluviatile, Juncus effusus, Menyanthes trifoliata can be found the under construction application of sewage treatment plant on highlands of the Western Carpathians (to 900 m.n.p.m., the average annual air temperature > of 5 °C and the time of lying of the snowy lid of 90 days in the year).