The generalized bioavailability model (gBAM) has been proposed as an alternative to the biotic ligand model (BLM) for modeling bioavailability and chronic toxicity of copper. The gBAM combines a log‐linear effect of pH on free Cu2+ ion toxicity with BLM‐type parameters for describing the protective effects of major cations. In the present study, a WHAM VII‐based gBAM for fish has been parametrized based on an existing chronic (30d‐mortality) dataset of juvenile rainbow trout. Overall, the chronic Cu gBAM developed here is a valuable alternative for the existing chronic Cu BLM for rainbow trout and performs sufficiently well to be used in risk assessment according to currently accepted standards of bioavailability model performance.