Data are presented on Stuckenia filiformis (Potamogetonaceae) records from new localities in the north of the Murmansk Region, i.e. in the Pasvik State Nature Reserve and its neighboring territories in the Paz River catchment. S. filiformis is a rare plant in the region listed in the Red Book of the Murmansk Region with status 3. It was found in 3 new localities: one within the nature reserve in the Paz River (Lake Salmijarvi), and the other two in the Paz River
catchment in Lake Kuetsjarvi and in an unnamed lake near River Kasesjoki. Additionally, the species was collected in two previously known localities. The conditions in the habitat were studied in all the sites. The resultant data brought about the conclusion that the distribution of the species in the studied area is limited by the TDS content of the water: S. filiformis occurs in waters with a 2–3 times higher TDS content compared to what is characteristic of
the whole area. This can be due to local features of the geological structure in places of carbonate rock outcropping or inflow of mineralized waters, but may also be a consequence of human impact on the water bodies, i.e. discharges from the mining and metallurgical industry.