Because amphipods are both ecologically important and relatively resistant to metals, they are interesting candidates to quantify the fraction of bioavailable metals in freshwaters. However, the accumulation strategies have to be defined for each metal/organism couple in controlled conditions in order to construct models characterizing the waterborne bioaccumulation. The biodynamic model predicts that the waterborne bioaccumulation is the result of a balance between the uptake of dissolved metals and the excretion. However, it is possible that the metal uptake saturates for high exposures due to a limited number of specific binding-sites within the organism. The metal bioaccumulation can be then described satisfactorily using a saturation model. Furthermore, the metal uptake can be reduced due to a competition of free metals for physiological sites with environmental ligands such as major ions found in freshwaters. It is thus necessary to characterize the influence of water chemistry on the bioaccumulation process to improve the prediction of these two models, coexisting in the literature but rarely compared.