Habitats important for biodiversity are being lost to construction projects, including hydroelectricity generation infrastructure, electricity transmission lines, new roads and railways, and industrial and urban development. The upper layer of water obtains oxygen from the atmosphere, whereas below 130-150 m the water is rich in hydrogen sulphide. As a result, about 87-90 per cent of the water is anoxic, i.e. devoid of oxygen, only the upper layers and shelf waters contain oxygen.