Scientists have now found tiny plastic particles in all of the Great Lakes.
The Duluth News Tribune reported they had previously found them in Lakes Superior, Huron and Erie last year.
Lorena Rios-Mendoza, assistant professor of chemistry at the University of Wisconsin-Superior, said Thursday their summer research has turned up found small concentrations also in Lake Michigan and Lake Ontario.
She says Lake Erie seems to hold the highest concentrations of plastics, probably because the particles float downstream from the upper lakes.
Rios-Mendoza says the plastic has also been found in Lake Superior sediment, meaning it's not just floating on the surface.
The researchers dragged fine-mesh nets across the surface of lakes. Some of the plastic can be seen only under a microscope.