As the topic of ocean plastic pollution continues to make headlines, scientists from Newcastle University are revealing that, like an iceberg, the issue is much larger with 99.9% of plastic pollution hidden below the surface of the world’s oceans.

Using computer models, researchers discovered that of the 393 million tons of plastic waste in the world’s oceans, just 246,000 tons of it are visible at the surface.

Over time, the plastic waste found floating at the water’s surface becomes bogged down by algae that begins to grow on the waste. Slowly sinking over time, the plastic ends up at the bottom of the ocean, typically covered by sediments making it impossible to locate the waste. Researchers estimate that each year, roughly 5 to 36 million tons of plastic are deposited in sediment.

However, no matter where it lands, the plastic is still problematic for marine life ingesting the material or becoming ensnared in it, according to researchers.

Alethea Mountford, a scientist behind the research, said: “There are loads of organisms still living on the sea floor, in the sediments, so they can eat the plastics. And we know there are chemicals released from plastic that can harm organisms like that — their reproduction, their feeding, it can make them starve to death.”