The Qinghai Lake, or Ch'inghai Lake, is the largest lake in China. It is in the Qinghai Province, which is where the lake gets its name. The lake has a surface area of . The lake is a alkaline salt lake. Its size has changed over time. During the 20th century, it became smaller, but has been getting larger since 2004. The average depth of the lake was in 2008. The deepest part of the lake was .