<p>This study aims to evaluate total concentrations and chemical forms of heavy metals (Zn, Cu, Cd, Pb and Fe) in surface sediments of the Bou Rmeda Lagoon, located at 23&#xa0;km from Sfax City (southern Tunisia). 24 surface sediment samples were collected and analyzed by inductively coupled plasma-atomic emission spectrometry. Metal contents of sediments in the lagoon exceed by far natural regional levels (except for iron chosen as natural tracer). Compared to Sediment Quality Guidelines, Zn concentrations of all samples were shown to be higher than Effects Range Medium values. Cu, Cd and Pb concentrations of most of the samples are between Effects Range Low and Effects Range Medium values. The analyzed metals (except for iron) present similar spatial distributions closely linked to the local hydrodynamic conditions. The highest values are located in the most sheltered zones. Two pollution indices were calculated from total heavy metal concentrations (Modified hazard quotient and modified pollution index). It revealed that studied sediments are heavily polluted with extreme severity of contamination. These results highlight the importance of hydrodynamic conditions which favor the accumulation of heavy metals in spite of the absence of local anthropogenic sources. The ecological risk was assessed by two indices. The modified potential ecological risk index calculated from total heavy metal concentrations implied a moderate-to-considerable risk while the individual contamination factor determined from concentrations of carrier fractions shows low risk. Indeed, chemical speciation indicated that heavy metals found in most residual phases reduce the environmental risk caused by anthropogenic activity.</p>