Nine large plateau lakes in southwest China's Yunnan Province have seen improved water quality amid continuous ecological restoration efforts, local authorities said Tuesday.

Located in the provincial capital of Kunming, Dianchi Lake, Yunnan's largest plateau lake, has seen its best water quality in the past 30 years, according to Pu Lifeng, deputy director of the Department of Ecology and Environment of Yunnan.

The surface water quality of Caohai, a part of Dianchi, was graded Class IV for the last two consecutive years, improving from Class-V in 2015.

Surface water quality in China is divided into five classes, with Class V being the worst and Class I being the best.

Ecological protection and restoration projects have also helped curb the decline in the water quality of Erhai Lake, a major tourist draw in the city of Dali in Yunnan. The water quality of Erhai remained between Class II and Class III in the past two years.

More than 20 billion yuan (about 3 billion U.S. dollars) has been invested in improving Erhai's environment over the past five years, official data showed.

Fuxian Lake in the city of Yuxi and Lugu Lake in the city of Lijiang, both famous tourist spots, have seen their water quality remain at Class I in the past five years.

Yunnan currently has only one lake of Class-V water quality, down from four in 2015.