As governments around the world grapple with the challenge of responding to increased plastic pollution, extended producer responsibility (EPR) policy, which shifts the responsibility for waste management of a product to producers, is quickly becoming a cornerstone of legislative approaches to this issue. However, the effectiveness of this policy has never been assessed in terms of reducing plastic marine debris. Understanding if a policy like EPR is having an effect requires collecting and analyzing information before and after a policy is introduced. Using British Columbia, Canada as a case study, we evaluate the influence of an EPR policy for packaging to reduce shoreline pollution. We use available citizen science data to demonstrate that there has been no reduction in pollution levels after the introduction of the policy. The findings also highlight some limitations when using citizen science data for a purpose it was not intended for. To effectively evaluate prevention of plastic pollution in the marine environment, plastic policy interventions require monitoring programs tailored to their specific requirements.