Taihu Lake, the country's third-largest freshwater lake in the lower Yangtze River region, has seen its water reach fairly good quality for the first time in the past 30 years, according to Jiangsu provincial department of ecology and environment.

Monitoring showed that the water quality of the lake stood at Grade III in 2024, the department said in a news release on Sunday.

China has a five-tier quality system for surface water, with Grade I the best. Water with a quality of Grade III is good enough for most aquatic organisms to live in. The quality of water can be considered as being fairly good if it reaches Grade III and above.

The progress is achieved thanks to persistent efforts of local authorities to treat the once heavily polluted lake.

Since 2007, over 300 billion yuan ($41 billion) of investment has been made into treating the water body, with pollution source management and pollution interception as key priorities.

In 2024, almost 6.4 million cubic meters of mud were dredged from the lake and more than 1.7 million metric tons of blue-green algae were cleared.