<p>Based on analysis of documents obtained in public databases and under freedom of information requests, this study assessed the Alberta Energy Regulator’s (AER) monitoring and management of bitumen tailings spills. The AER’s claims of no environmental impacts at any tailings spills lack corroborative environmental data. Claims of perfect spill recovery in 75% of tailings spills are not supported by credible evidence. AER’s spill footprints are unrealistically small relative to the spill volumes. The reported number of spills and total spill volumes are underestimates of the true rates. Reported spill locations are imprecise and inaccurate. For many spills, incident dates are not being accurately reported. The AER claim of routine inspections of spills is not supported by data; only ~ 3.2% of reported tailings spills are inspected. The AER’s tailings spill data lack the ecological, biological, and chemical data required to assess and manage the environmental impacts of tailings spills. Approximately 41–54% of tailings spill sites with photographic documentation showed evidence of environmental harm. If similar rates of harm in relation to tailings spill volumes apply to spills lacking photographic evidence, environmental harm would be inferred in 23–36% of those spills. The AER’s failure to gather credible and relevant environmental data, conduct routine on-site inspections, and protect ecosystems from harm is inconsistent with its regulatory responsibilities. As a result of chronic mismanagement since 1967, ecological risks will persist for decades. The true magnitude of the ecological impacts of tailings spills may never be known.</p>