Salinity is an important factor that affects the ecological risks of contaminants, especially metals, in the estuarine environment. Copper (Cu) is one of the metals with the highest risk due to its widespread contamination and its high toxicity. The effects of salinity on Cu toxicity have thus received much attention. However, generalizing the effects of salinity for risk assessment of Cu is still a challenge, mainly due to the complex effects of salinity and the substantial interspecies differences. In this study, we used the toxicokinetic-toxicodynamic model as a unifying framework for simulating both the bioaccumulation and toxicity of Cu under various salinities and in three representative euryhaline species, i.e., a fish (Oryzias melastigma), a waterflea (Moina mongolica), and a clam (Potamocorbula laevis). The stable-isotope-tracer technique was used to measure the uptake and depuration of Cu in the organisms. At low Cu levels (10-20 μg L⁻¹), Cu uptake rates generally decreased with the increase of salinity; at high Cu levels (~500 μg L⁻¹), the inhibitive effects of salinity became less apparent, presumably due to the saturation of Cu uptakes sites. Nevertheless, different patterns were observed among species: non-monotonic change of Cu uptake was observed in the fish and waterflea, suggesting that the effects of salinity were more than geochemical effects. The effects of salinity on Cu bioaccumulation could not be directly translated into the effects on Cu toxicity; the lowest Cu toxicity was observed at intermediate salinities in all species. The decoupling between Cu bioaccumulation and toxicity was due to the changes in the intrinsic sensitivity of the organisms under different salinities, which could be measured by the two toxicodynamic parameters, i.e., the internal threshold concentration and the killing rate. The toxicokinetic-toxicodynamic model provides a method for separating and quantifying the multiple effects of salinity and thus can be served as a tool for better managing the risks of contaminants in the estuarine waters.