Pearl River Estuary
The bell-shaped Pearl River Estuary receives and carries most of the outflow from the Pearl River, the common name for a complex system of rivers in the southern Chinese province of Guangdong. The estuary is nearly 37 miles (60 km) long, and its width increases from 12 miles (20 km) at its head to about 30 miles (50 km) at its mouth. To the north and west of the estuary is a delta, formed from the confluence of the Xi Jiang and other rivers of the Pearl River system. Together, these rivers discharge an average of 2.6 million gallons (10 million liters) of water per second into the South China Sea. Mostly less than 30 ft (9 m) deep, but containing some deeper dredged channels, the Pearl River Estuary has a tidal range of 3–6 ft (1–2 m). It drains water from some of the most densely populated areas of China, and so is severely polluted with sewage and industrial waste. About 617 million tons (560 million metric tons) of domestic waste and 2.2 billion tons (2 billion metric tons) of industrial effluent enter the estuary each year. Over the past 20 years, this pollution has led to frequent algal blooms that threaten local fishing and aquaculture. Pollution is also a threat to the 1,400 Chinese white dolphins that live in the estuary.