Plastic debris beaching on two remote Indian Ocean islands originates from handful of Indonesian rivers

Abstract Large amounts of plastic waste from non-local sources (>200 tonnes) wash up on Christmas Island and the Cocos Keeling Islands, two remote Indian Ocean islands, every year. Local communities on these islands organize beach clean-ups regularly to tackle this problem and, because their waste systems cannot handle the enormous amounts of plastic, predominantly incinerate the collected waste. However, as long as plastic waste keeps entering the ocean, beach clean-ups alone cannot be sustained. The first crucial step to solving this problem is to determine the main sources of plastic waste to the islands. In this study, we simulate the transport of floating plastic waste to determine the main riverine sources of plastic reaching the islands. We find that the majority of simulated plastic waste comes from just 4 Indonesian rivers: the Solo, Brantas, Ci Tanduy, and Wai Sekampung. We suggest that further numerical and field studies, as well as potential river clean-up efforts focus on these rivers to stop plastic waste inundating Christmas Island and the Cocos Keeling Islands.