Caohai Lake (Chinese: 草海; pinyin: Cǎo Hǎi, Sea of Grass in Chinese) is a natural water-body situated in Northwest Guizhou Province of southwest China.

However, as a result of drainage, cultivation, and climate change during the last few decades, the lake area has contracted to only 5 km2 (1.9 sq mi).

Cao Hai Nature Reserve is an Important Bird Area.

[1] The lake area is the largest and most important wetland of Southwest China, providing wintering grounds for black-necked cranes, the only crane species inhabiting plateaus left in the world.

In addition, the lake is also inhabited by 184 bird species, including common cranes, hooded cranes, white storks, black storks, bar-headed geese, golden eagles, eastern imperial eagles, white-tailed sea-eagles, and ruddy shelducks.