Muri Lagoon is a kilometer-wide (0.62 miles) lagoon on the southeastern coast of Rarotonga, in the Cook Islands. It is a significant tourist attraction to the region, despite being heavily polluted with nitrogen from agricultural runoff and leaking septic tanks — so much that it was declared a natural disaster in 2015. Rarotonga is the largest and most populous of the 15 Cook Islands, a self-governing country in the South Pacific Ocean.