Due to metals posing a risk to aquatic organisms, regulators have been interested in monitoring metals in aquatic environments, primarily determining the influence of speciation and bioavailability. Passive diffusion devices, like Diffusive Gradients in Thin-films (DGT), could be used as a simple, cost-effective, in situ sampling device that allows regulators to measure the free and labile metal fraction in natural waters. We evaluated whether DGT can accurately predict copper bioavailability to two freshwater species, fathead minnow (Pimephales promelas) and yellow lampmussel (Lampsilis cariosa). Organisms and DGT were exposed to environmentally relevant copper concentrations over a range of water chemistries: soft and hard water, addition of natural organic matter, and metal mixture with lead. Effect of deployment duration was also explored. Correlations of organism accumulated copper with DGT measured fraction suggested strong predictive ability for fathead minnow (r2 0.662-0.929), but less for yellow lampmussel (r2 0.224-0.711).