Before what appears to be part of Malaysia Airlines Flight 370 floated ashore on Réunion this summer, more than a year of false reports pointed to another issue: the mysterious flow of refuse and debris in the world’s oceans.

But this stuff isn’t floating around at random — it’s also forming massive, nearly invisible garbage “islands” at five places in the oceans.

NASA decided to visualize how these dumps are forming and you can see what they learned in the video here, posted in a Slate article.

Scientists don’t know how big they are because an estimated 70 percent of the trash sinks, and much of it is tiny bits of non-biodegradable plastic floating out of sight just below the surface. The garbage is inarguably a threat to marine life and the health of the oceans.

NASA started out by tracking ocean buoys. There are lots of them, and NASA factored in how long each one has been in the water and the location from which it was launched. Ocean currents have collected most of them into five areas — and guess what those areas are? Inevitably, the same locations as the garbage islands.

To confirm its findings, NASA next took a look at a computer model of ocean currents. It set thousands of virtual particles adrift to see where they’d wind up. They ended up in exactly the same spots as the buoys. And the garbage.

Ocean trash largely gets launched by winds that blow it offshore, and from ships traversing the waters. By supporting beach-cleanup efforts and tighter standards for oceanic trash disposal, the public can help reverse the dangerous tide.

This post originally appeared here.