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A sample of some of the smaller items collected by University of Toronto assistant professor Chelsea Rochman and her lab class.Chelsea Rochman

Almost 600 plastic fragments, 187 bottles, 133 litres of Styrofoam and 43 straws: 31 kilograms of trash in all.

That’s what Chelsea Rochman, an assistant professor of ecology at the University of Toronto, and her team found floating down Toronto’s Don River in slightly more than two weeks – and that’s just what they were able to count.

“We couldn’t get through all of it,” Dr. Rochman said.

The real numbers are higher still, she said, since some of the trash simply floats under or around the Don River booms – a line of logs that Ports Toronto secured in place across Keating Channel.

From June 29 to July 16, Dr. Rochman and a group of U of T students let trash build up on the booms, then collected it all under the muggy July sun. The smell was “terrible,” she said.

She was surprised by the sheer amount of trash, she said, but not by what it was made up of.

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Some of the smaller items collected in the study of trash flowing down Don River in Toronto into Lake Ontario.Chelsea Rochman

“As we’re thinking about single-use items like straws and plastic bags being banned or taxed, it makes sense, because that is what we’re seeing in our environment,” Dr. Rochman said.

Over the course of a year, she calculated that 12,775 plastic fragments would float down the Don River and into Lake Ontario, along with thousands of bottles, food wrappers, straws and wayward balls kicked into the river. In all, 663.4 kilograms of garbage.

While companies are the biggest polluters, Dr. Rochman said the majority of the Don River garbage she collected comes from individual litter. A cigarette butt thrown on the ground in downtown Toronto can easily make its way into a storm drain when it rains, she said – and those storm drains empty directly into rivers and tributaries.

It rained in Toronto just after they collected the trash, she said, and the booms were once again loaded with trash.

“We can blame industry all day … but human behaviour is also a big part of this issue.”

Rivers are one of the main conduits that take take garbage and other pollutants into major bodies of water, Dr. Rochman said. Since the Don River has the highest percentage of urban area surrounding it of any river in Canada, it’s the perfect place to study the effects of human pollution.

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Wood and trash debris accumulated by the Don River booms.Chelsea Rochman

Plastic in an ecosystem such as Lake Ontario can kill fish and affect their reproductive systems so they can’t replenish their own stock, she said.

“That’s where our motivation all comes from,” she said. She said she is currently working with Ports Toronto to develop better trash-catching infrastructure for the Don River.

Dr. Rochman hopes people keep the environment in mind the next time they’re tempted to throw trash on the ground, or even in the wrong bin. One of the most important things a resident of a city like Toronto can do, she said, is to learn the waste management system and try to consume as little non-recyclable material as possible.

“I think a lot of people just think about our waste [going] away, and they never stop to think, where is away?”