During monsoon season, the Mekong River on the border between Cambodia and Laos increases in volume by a factor of 20, flooding the Si Phan Don wetlands and creating an area of turbulent rapids 11-14 km (7-8.5 miles) wide. The flow rate here is twice that of Niagara Falls, with 10 million litres metres of water thundering its way through a maze of channels between the area's many islands every second. The Mekong River threads through 4,184 km (2,600 miles) of Indochina, taking in China, Myanmar (Burma), Laos, Thailand, Cambodia, and Vietnam, and drains into the South China Sea. Two-thirds of Cambodia's rainfall occurs during the wet season (May-October), and during the peak (July-September) it will rain two out of every three days. Si Phan Don means "Four Thousand Islands".