Water contamination by heavy metals is a serious global problem due to increased environmental and health-related issues. In this study, we have comparatively investigated the heavy metal concentrations and mineral nutrient levels in Karasu river sediments and in plants samples of Phragmites australis (Cav.) in order to assess the biomonitoring capacity. Plant and sediment samples were collected from four different localities along Karasu River, and those samples were analyzed in terms of heavy metals such as Fe, Zn, Mn, Ni, Cr, Cu, Pb, Co and Cd, and in terms of mineral elements such as K, Ca, Mg, Na, Al, and B using ICP-OES. In addition, lipid peroxidation, chlorophyll and carotenoid levels in plant samples were also checked. Sediments in Karasu River contained high concentrations of Ni and Cr metals. Moreover, P. australis showed hyper-accumulation for Cd and Zn in root and leaf samples, respectively. Although there was no significant difference in chlorophyll amounts among locations, lipid peroxidation was found to be high in samples taken from ilic.