The investigation of bottom sediments in oxbow lakes was conducted in the free-flowing, meandering section of the Łyna River
in N Poland. Seven oxbow lakes, differed by a degree of hydrological connectivity with the river channel, were chosen for the
present study. In samples taken from 21 sediment profiles, particle size distribution, pH, bulk density, CaCO3, organic matter,
total organic carbon as well as total forms of N, P, K, Ca, Na, Mg, Mn and Fe were determined. The gradient of decreasing
exchange of water between a floodplain lake and the river channel influenced the decrease in sand fraction and the increase in
organic matter content. At the water inflow into the semi-lotic and lotic oxbow lakes, the decrease in transporting strength of the
river occurred particularly favorable for mineral matter accumulation. A significant decrease in majority of nutrients and
macroelements was noted along with vertical sediment profiles of each oxbow. Our results showed floodplain lakes have ability
to remediate water quality by trapping catchment-derived substances. Thus, they play an important role in the purification of
flowing waters.