The Pearl's Green Sickness
Once called the "Sparkling Pearl of the Plateau," Dianchi Lake is a 3.2-million-year-old tectonic lake and the largest in Yunnan province. As recently as the 1950s, its waters were clear and teeming with native species. Decades of rapid urbanization and industrial growth around the city of Kunming transformed it into one of China's most polluted lakes. By the 1980s, enormous quantities of untreated industrial effluent, municipal sewage, and agricultural runoff high in phosphorus and nitrogen poured into the lake.
This nutrient overload triggered a condition called hypereutrophication. The water quality plummeted to "inferior to Grade V," the worst level in China's water grading system, making it smelly and murky for human contact. The primary symptom was massive, persistent blooms of blue-green algae, or cyanobacteria, particularly the species Microcystis aeruginosa. These blooms formed a thick green blanket across the water's surface, blocking sunlight from reaching submerged plants. As the algae died and decomposed, bacteria consumed all the available oxygen, creating hypoxic dead zones and decimating the lake's native fish populations. The lake's biodiversity crashed; aquatic plant species dropped from over 100 to fewer than 20.
An Engineered Green Liver
Early efforts to clean the lake, including dredging and chemical treatments, proved costly and insufficient. A more sustainable, nature-based solution began in 2008 with the large-scale construction of an ecological belt around the lake. Today, this green buffer consists of over 20 wetland parks covering a total area of 33.3 square kilometers. This system is a giant "green liver" for the lake, intercepting and purifying polluted water before it enters the main body.
These are not wild marshes but engineered ecosystems. Water from incoming rivers and even treated wastewater from Kunming's purification plants is routed through them. The water slowly filters through a network of ponds, channels, and soil layers planted with specific vegetation. Plants like water hyacinth (Eichhornia crassipes), cattails (Typha orientalis), and reeds (Phragmites australis) are exceptionally good at absorbing excess nitrogen and phosphorus from the water, a process known as phytoremediation. In 2023 alone, the Dianchi basin wetlands absorbed an estimated 1,324 tons of total nitrogen and 74 tons of total phosphorus. This biological filtration has helped the lake's recovery. Water quality has stabilized at Grade IV, a significant improvement, and the days of severe algae blooms have been markedly reduced.