Off Africa’s eastern coast, north of Madagascar, lies Aldabra Atoll, a cluster of coral islands that surround a tropical lagoon.

Aldabra is a UN World Heritage Site that’s home to a stunning array of wildlife, including tens of thousands of wild giant tortoises, far more tortoises than in the Galapagos Islands. Sir David Attenborough, the documentary filmmaker, has called Aldabra “one of the wonders of the world.” The atoll is exceedingly difficult to visit, not only because it’s so remote, but also because new arrivals must contend with a $225 per-visitor daily environmental impact fee — as well as piracy in the region.

This wild, protected place is also, according to newly published research from Oxford University, littered with over 500 tons of plastic waste.