It is a freshwater fault lake at 1,886.5 m (6,189 ft) above sea level. The lake covers 298 km2 (115 sq mi). It is 39 km (24 mi) long from north to south, and the average depth is 4.4 m (14 ft). It is the eighth largest lake in China and the largest in Yunnan Province.
Pollution is a major problem for the lake. In the city of Kunming, the capital of Yunnan province, parts of which are subtropical, there was traditionally no talk of water shortage, since the city is right next to one of Asia's biggest freshwater lakes. But 90 percent of Kunming's wastewater was pumped untreated into the lake until the first wastewater plant was built in 1990. In addition, much of the marsh system around the lake was destroyed during the Great Leap Forward in a misguided effort to raise rice production by filling the marshes in with trucked-in soil. Agricultural runoff is also a major problem.
The lake water is now undrinkable despite several billion US dollars having been spent trying to clean it up. Some experts predict that over 55% of the lake's fish population has been killed off by this disease-ridden type of pollution.The water in the lake is rated Grade V (the worst grade) which makes the water unfit for agricultural or industrial uses.