GPS Drifters Reveal How Urban Wind Currents Spread Plastic Pollution Across Ontario

In a groundbreaking study by researchers from the University of Toronto Scarborough and the University of Toronto Trash Team, the movement of macroplastic debris in Toronto Harbour was tracked using GPS-enabled bottle-shaped drifters, offering one of the most detailed looks yet into how plastic pollution behaves in freshwater urban environments. Designed to emulate common plastic litter, the drifters provided real-time data as they floated through the harbour and into Lake Ontario. What emerged was a compelling portrait of a plastic pollution pathway dominated by wind rather than water currents, with important implications for waste management in urban watersheds. The findings, published in the Marine Pollution Bulletin, underscore Toronto’s role as both a local and regional source of aquatic plastic pollution, as well as the urgent need for targeted infrastructure to curb its spread.

Plastics on the Move: Following the Wind

At the heart of the study was the deployment of 66 GPS-tracked drifters across 21 locations in Toronto Harbour between April and July 2021. These modified Blender Bottles were chosen for their buoyancy and visibility, containing GPS units that transmitted their positions at regular intervals. The data showed that the drifters’ movements were largely dictated by wind direction and speed. Approximately 75 percent of the drifters became stranded in various pockets within the harbour, such as under docks and inside slips and channels. However, around 22 percent escaped the harbour, mostly through the West Gap, while a few traveled via the Outer Harbour. These movements reflected not just local wind patterns but the dynamic interaction between atmospheric forces and shoreline features.

What was particularly striking was how quickly and how far some drifters traveled once they left the confines of Toronto Harbour. One made a remarkable 290-kilometre journey across Lake Ontario to Rochester, New York, in just 14 days. Another reached Hamilton in under three days, while a third meandered toward Ajax. These long-distance voyages highlighted that plastic pollution originating in urban harbours can extend its reach far beyond city boundaries, becoming a lake-wide, and potentially transboundary, issue.

Measuring the Wind Factor

A key innovation of this study was the calculation of the “wind factor,” the ratio of the drifter’s speed to the wind speed. Historically, water current modeling assumed that surface currents move at 2 to 5 percent of wind speed. However, the GPS data revealed that in the open waters of Lake Ontario, drifters sometimes traveled at speeds up to 50 percent of the wind speed. Even within Toronto Harbour, the wind factor was consistently higher than previously estimated, owing to the high windage of the drifters—that is, the large portion of their structure sitting above water and directly interacting with the wind.

Inside the relatively shallow and sheltered harbour, the drifters traveled at an average speed of 3.5 cm/s, while in the open lake, they reached speeds of 24.2 cm/s. The disparity highlights how shoreline complexity, harbour morphology, and local obstacles such as buildings and vegetation can dampen wind-driven transport. In contrast, the open waters of Lake Ontario allow uninterrupted wind flows, creating conditions for stronger, longer-lasting currents and even “inertial waltzes”—circular drift patterns formed after winds cease, influenced by the Earth’s rotation.

Plastic Debris and Urban Shorelines

The study didn’t just track where plastics go, it also revealed where they tend to accumulate. Drifters consistently became stranded in sheltered areas, such as slips, channels, and under piers and boardwalks. These findings align closely with visual audits by Sherlock et al. (2023), which documented large accumulations of floating plastic debris, especially bottle caps and containers, in western areas like the Peter Street Basin. Interestingly, the expected accumulation along eastern shorelines due to prevailing southwesterly winds did not materialize in 2021. That year, atypical weather patterns brought frequent strong northeasterly winds, pushing debris into different zones than historical trends would predict.

Another important discovery was that a drifter collected by city waste management was tracked all the way to a landfill site, indicating that human intervention, sometimes unintentional, can also affect plastic transport pathways. Others were likely destroyed by shipping activity or trapped under docks, becoming untraceable. In total, about 20 percent of the drifters were unrecoverable, pointing to the challenges of monitoring real-world pollution in complex environments.

Engineering Smart Cleanup Solutions

Beyond mapping plastic pathways, the research offers practical strategies for mitigating pollution. Areas with high-volume transport, such as the Don River Mouth and Shipping Channel, are prime candidates for active trash capture devices like trash wheels, which can process large amounts of debris. More stagnant accumulation zones under piers, in slips, and along urbanized shorelines could benefit from passive systems like Seabins, which float and collect waste in localized areas. The study also recommends frequent manual cleanups along naturalized shorelines, such as those around the Toronto Islands, where floating debris tends to accumulate more slowly but persistently.

These recommendations are not merely theoretical. They reflect direct observation and field-based evidence showing that the location, morphology, and wind exposure of different harbour regions strongly influence the behavior and accumulation of floating plastic waste. This kind of evidence-based planning can significantly improve the efficiency of municipal waste management programs and reduce the environmental footprint of urban centers.

A Wake-Up Call for Great Lakes Cities

Perhaps the most urgent message from this study is that even if most urban plastic pollution remains local, a significant fraction can travel far beyond city limits. Toronto Harbour is not just a sink for plastic waste—it’s a source. With some plastics making it across international borders, the implications for freshwater stewardship are profound. The variability in wind and current patterns means that cities around the Great Lakes cannot assume their waste stays within their jurisdiction. But this variability also offers a hopeful note: targeted interventions in source zones like Toronto Harbour can ripple out, reducing the overall burden on Lake Ontario and the broader Great Lakes ecosystem.

In sum, the study marks a significant leap forward in our understanding of freshwater plastic transport. By blending simple technology with scientific rigor, the University of Toronto researchers have mapped not only how plastics move, but also how cities can act to stop them. The message is clear: with smart design and localized action, the tide of plastic pollution can be stemmed before it becomes an unmanageable lake-wide problem.