Tiny pieces of plastic – each about the size of a grain of sand – are posing a huge threat to marine life in the Great Lakes.

For the past two summers, researchers from an organization called 5 Gyres have been collecting water samples from the Great Lakes.

They used fine-mesh nets to skim the surface of the water.

When they looked at what they had collected, they found thousands of tiny plastic beads, each less than a millimetre.

At first the scientists didn’t know where these “microbeads” came from. Then they used an electron microscope to compare them to products such as face and body washes or toothpaste that people use to help scrub and polish our skin and teeth.