Plastics are a ubiquitous environmental pollutant. From fibers shed off clothing to paint flaking off boats, plastics of all sizes serve as vectors, mobilizing hazardous chemicals through the built and natural environments. Communities around the globe are engaged in efforts to mitigate and better understand plastic pollution in their neighborhoods. Scientific research on the topic is rapidly growing, but with nearly 400 million tons of plastics manufactured each year, opportunities to accelerate this knowledge building are essential. In this dissertation I investigate how existing efforts to better understand plastic pollution can be made more efficient, inclusive, and useful. Over the course of three studies, I focus on microplastic (<5mm) pollution of surface waters and macroplastic (>25mm) pollution of rivers and city streets. Analyzing existing datasets—including one of published scientific research, a second from a community group, and a third collected by citizen scientists—I characterize opportunities for synthesis and partnership. In the first study (Chapter 2), I find existing scientific data can be leveraged for inter-study comparisons and regional syntheses if contamination can be fully quantified and methods are thoroughly documented. In the second (Chapter 3), I find community-sourced data on floating trash answers questions of interest to both managers and scientists, particularly if placement of the trash traps involved is optimized through researcher-community collaboration. In the final chapter (Chapter 4), I identify opportunities to enhance citizen science data collection methods for street litter and find litter density data currently produced by another non-traditional and underutilized data source, municipal litter audits, to be scientifically sound and relevant to key research questions.