Oil sands tailings pond sediments and sediments from the Athabasca River were assessed for embryo‐larval toxicity in fathead minnows and walleye. No effects were seen in fathead minnow eggs and larvae exposed for 20 days to 5 sediments from Athabasca River at concentrations up to 25 g L‐1. Two of three tailings pond sediments were toxic to fathead minnows at concentrations as low as 0.2 to 1 g wet wt L‐1. All three tailings pond sediments reduced growth (lengths) of larvae. Nine of 18 polycyclic aromatic hydrocarbons (PAHs) measured in tailing pond sediments were above the CCME Freshwater Sediment Quality Guidelines, with phenanthrene being the highest at 19 μg g‐1dry wt. Total PAHs were up to 56 μg g‐1 dry wt. Total naphthenic acids in tailings pond sediment were up to 16 μg g‐1. River sediment had up to 2.6 μg g‐1 naphthenic acids and up to 0.25 μg g‐1 total PAHs. Results are preliminary, and we cannot at this time say what is causing the observed toxicity in fathead minnow larvae. Assessment is continuing with exposure of walleye eggs and larvae, to compare their relative sensitivity to these sediments, and to assess the potential causative compounds.