As part of the Joint Canada-Alberta Oil Sands Monitoring Plan, the toxicology of natural and oil sands related environmental samples was studied. One of the goals of the toxicity tests is to examine pathways and sources of contaminants that may be causing effects in wild fish and invertebrates. Samples were collected from sites where wild fish health assessments and invertebrate communities were assessed. In this way, linkages could be made between wild invertebrates and fish, in comparison to controlled studies of lab fish exposed to certain components of the environment (sediment, water, groundwater, and snowmelt). Embryo-larval fathead minnows were used to assess the chronic toxicity of the following environmental samples: river sediments, river waters, groundwaters, snow melt waters, spring freshet waters, and suspended sediments collected in the vicinity of the Canadian oil sands. Samples were collected in 2009- 2013 from rivers near oil sands processing facilities along the Athabasca River and tributaries in areas of oil sands development, and compared to samples collected far from sites of oil sands mining and processing. Fertilized fathead minnow eggs were exposed for 21 days (through hatch to 7-15 days post-hatch) to samples in dose- response gradients. Most environmental samples caused no effects in larval fish in 21 day assays. Samples that caused effects in larval fathead minnows were several snow melt samples, several groundwaters, sediments from the Steepbank and Ells Rivers, and waters from the Muskeg River. Some of the toxic samples were from sites close to industry (Steepbank River sediments, snow samples close to stacks, Muskeg River waters). Other samples (groundwaters, Ells River waters) showed toxicity far from oil sands activities, with effects in lab fish seen at “background’ sites where natural oil sands weathering or water movement thru bitumen occurs. Samples were analyzed for naphthenic acids, PAHs, C1-C4 alkylates PAHs, and metals. Sites where sediments and waters were toxic in lab fish bioassays are being assessed to determine whether wild young-of-year fish are abundant and growing normally in these areas of potentially toxic sediments or waters. The results of this work will help guide future studies and locations to sample wild fish and invertebrates to fully assess environmental health in the oil sands area.