The diversion of the Amu Darya and Syr Darya rivers for irrigation has shrunk the Aral Sea dramatically. The sea's surface area shrank by approximately 60%, and its volume by 80%. In 1960, the Aral Sea was the world's fourth-largest lake, with an area of approximately 68,000 km² and a volume of 1100 km³; by 1998, it had dropped to 28,687 km², and eighth-largest. Over the same time period its salinity has increased from about 10 g/l to about 45 g/l. As of 2004, the Aral Sea's surface area was only 17,160 km², 25% of its original size, and still contracting.