Dian Lake

Dian Lake, also known as Dianchi, Lake Dian and Kunming Lake, is a fault lake located on the Puduhe-Xishan fault in Kunming, Yunnan, China at 24°23′–26°22′ N, 102°10′–103°40′ E. Its nickname is the "Sparkling Pearl Embedded in a Highland" (pinyin: Gāoyuánmíngzhū). It is the model for the Kunming Lake in Beijing's Summer Palace. Its name is the source of Yunnan's Chinese abbreviation.

Dian Lake is a shallow freshwater fault lake. The Lake is 40 km long, running from north to south, and has an average width of 7 km with the widest point being 12.5 km. The lake is 1886 meters above sea level and has 150 km of coastline. The lake's drainage area has a subtropical plateau monsoon climate, with an average annual temperature of 14.4 °C, a frost-free period of 227 days, and an annual precipitation of 1036 mm. The lake covers 298 km2. The lake has an average depth of 4.4 m, and is divided into two parts by an artificial dike. The northern end of the lake is called Caohai (pinyin: Cáohǎi) and has a surface area of 7.5 km2 and an average depth of 2.5 meters. The southern end of the lake is called Waihai (pinyin: Wàihǎi) and has a surface area of 292 km2 and an average depth of 4.4m. The water flows out of the lake to the west via the Tanglang River (Chinese: 螳螂江; pinyin: Tángláng Jiāng) which eventually joins the Yangtze River before finally reaching the Pacific Ocean. Dian Lake is the sixth largest lake in China and the largest lake in Yunnan Province.

Etymology
The Chinese character for the lake is a phonosemantic compound of the radical ("water") and the character, whose current pronunciation is zhēn but whose Old Chinese pronunciation has been reconstructed as *tin in Baxter–Sagart system. The character was first found in the Records of the Grand Historian as the name of Dian Kingdom. Modern studies suggest that the element "Dian" is derived from the language of the ancient extinct Bo people and means basin. The character 滇 was use as the name of the lake since the Han dynasty set "Dianchi County" (滇池县) in 109 BC.

History
Dianchi Lake was the site of the capital of the independent kingdom of the Cuan (爨) during the first millennium AD. At that time, it was known as Kunchuan (昆川)..

Between 1958 and 1970, under the CCP's agriculture strategy of "Taking grain as the key link", approximately 54 square kilometers of Dianchi Lake marshland were reclaimed to expand industry and agriculture in the Kunming basin. December 28, 1969, a rally for "reclaiming land from the sea" was held in Kunming's Dong Fang square with 100,000 soldiers along with students and factory workers were mobilized to "fight a war of annihilation to take farmland from Dianchi Lake." The participants shouted the heroic slogan "March to Dianchi Lake! Take grain from Dianchi Lake!". Reclamation efforts were led by People's Liberation Army Lieutenant General Tan FuRen. Immediately after taking office Tan FuRen announced Dian Lake would be a model for the national "reclaiming land from the sea" campaign. The goal was to reclaim 30,000 mu (20 Square kilometers)of land from Dianchi Lake to develop agriculture and make grain the mainstay. Tan FuRen personally spearheaded the reclamation project until his death by assassination in 1970.

Pollution
Pollution is a major problem for the lake. Yunnan Province has long been primarily agricultural, but the Dianchi basin has witnessed high industrial growth and boasts the highest population density within Kunming City

In the late 1990’s to early 2000’s, Lake Dianchi was identified as one of the 3 top water pollution concerns in China. The pollution peaked in 2009 at which time Dianchi lake was classified 'worse than a Stage 5' (too dangerous for human contact). Ninety percent of the city of Kunming's wastewater was dumped untreated into the lake until the first wastewater plant was built in 1990. Some experts estimated 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. The China Environmental Statistical Yearbook data reported that in 2013, 400 million tons of municipal sewage and 8 million tons of industrial waste water, were dumped into Dianchi lake of which only 1.5 million tons of which was treated before dumping. As of 2020, the water in the lake was still rated Grade V, but is deemed to meet the functional requirements of water environment.

Historically, Dianchi played important role in regulating the microclimate of the surrounding area. It contributed to the productivity of Yunnan Province's industry, agriculture, husbandry, and fisheries. Because Dianchi is a relatively closed lake with a slow water-exchange rate and low self-purification capacity it is particularly susceptible to harmful algal blooms and heavy metal contamination. From 1966 to 1970, the lake reclamation project caused severe damage to marsh wetlands in the Caohai area, which with large amounts of urban sewage and industrial wastewater traditionally discharged into the lake, exceeded its self-purification capacity and caused serious pollution. It has also been badly affected by cyanobacteria outbreaks in recent decades. To control the pollution of Dianchi, the Chinese government listed it as a national sewage treatment project in the ‘‘Three Rivers and Three Lakes’’ (Liaohe, Huaihe, Haihe, Taihu, Chaohu, and Dianchi) scheme launched in 1995. The extensive land reclamation and urbanization projects have had long-lasting impacts on Dianchi Lake, necessitating ongoing rehabilitation and pollution control efforts to restore the lake's ecological balance. As a result, some wetland parks have been constructed in the lakeside zone to purify the water and create leisure areas for citizens. Wetland parks are mainly in the form of oxidation ponds. They are small water bodies with such aquatic plants as Phragmites australis, Typha orientalis, Acorus calamus, Eichhornia crassipes, Lemna minor, and Pistia stratiotes; outside the ponds, there are trails, trees, and lawns.

Biodiversity
Together with other Yunnan lakes (Fuxian, Qilu, Yangzong, Xingyun, and Yilong), Dian Lake is recognized as an ecoregion. Among three major Yunnan lakes with a high number of endemics, the other two being Fuxian and Erhai, the most drastic loss of biodiversity has been seen in the Dian. Of the 25 native fish species and subspecies in Dian Lake, 10 are endemic to the basin: Acheilognathus elongatus, Anabarilius alburnops, Anabarilius polylepis, Cyprinus micristius micristius, Liobagrus kingi, Pseudobagrus medianalis, Silurus mento, Sinocyclocheilus grahami, Sphaerophysa dianchiensis and Xenocypris yunnanensis. Today, the only endemic fish known to survive in the lake itself is Anabarilius alburnops, but it is endangered. The remaining have not been recorded there since the 1990s or earlier, and most of these are likely extinct. Two other species, Schizothorax grahami and Yunnanilus nigromaculatus, are endemic to the general region, but have also disappeared from Dian Lake itself. Among the non-endemic natives, only gold fish and Asian swamp eel still live in Dian Lake. In contrast to the status of the natives, the lake is now home to more than 25 introduced fish species.

The Yunnan lake newt (Cynops wolterstorffi) was endemic to the lake, but it has not been seen since 1979 and is considered extinct.

Many native hydrophytes have also disappeared from the lake.