The Ganga has been rated as one of the most polluted rivers in the world. A World Commission on Water states that only three per cent of the Ganga water is safe to drink. The water levels in the river are so depleted and polluted that the Sunderbans wetlands and the mangrove forests in the Ganga delta face a serious threat of extinction. The study, supported by the World Bank and the United Nations, discovered that more than half the world's rivers are severely polluted or are rapidly drying up.