BEIJING -- Freshwater jellyfish were spotted in the limpid water of Beijing's Huairou reservoir earlier this year -- a rare sight for local hydrologists as this aquatic life form had disappeared from the capital city for more than 20 years.

"I was totally amazed at seeing freshwater jellyfish in Huairou," recalled Guo Wei, laboratory director at the Beijing Hydrology Center.

With a bell-shaped body of about 1.5 centimeters in diameter, this tiny and short-lived aquatic species is known to be very particular about its dwelling: a pellucid water body coupled with the right water temperature and a sound natural environment.

"The freshwater jellyfish is a veritable 'water-quality detector,'" Guo said.

Besides Beijing, this fanatic for cleanliness has also been reported in the waters of other parts of China, including the city of Wuzhishan in Hainan, Dalian in Liaoning, and Chengdu in Sichuan Province.

Other than freshwater jellyfish, endangered aquatic animals such as finless porpoises are also recovering their populations in China's clearer rivers and lakes as the country has ramped up efforts to enhance water conservation.

Water management has never been an easy task in China. Difficulties ahead include uneven water resource allocation, frequent floods and droughts, and the arduous task of nurturing its large population with just 6 percent of global freshwater resources.

China needs to strike a delicate balance between guaranteeing growing water usage and human activities along the waterways and the imperative of addressing challenges such as water pollution, overfishing, and biodiversity loss.

In 2021, a 10-year fishing ban was launched in pivotal waters of the Yangtze River to increase the populations of aquatic creatures.

More than 200,000 fishermen from 10 provincial-level regions along the river thus bid farewell to their centuries-old way of life and moved ashore. Many of them later joined fish protection teams, patrolling along the river to stem illegal activities.

"I have to admit that my work is kind of strenuous, but I volunteered to shoulder the responsibility to ensure that our descendants can live along the Yangtze River with a good environment," said Zhang Song, who had earned a living by fishing since 2000, but later became a member of a local fish protection team in southwest China's Chongqing.

China has also implemented river chief and lake chief systems, in which government heads are designated to be in charge of protecting water bodies within their jurisdiction. More than 1.2 million river chiefs and lake chiefs have been appointed so far.

Preliminary progress has been achieved. The number of finless porpoises, a key species for measuring the ecological environment of the Yangtze River, reached 1,249, up 23.42 percent from five years ago, according to a scientific expedition in 2022.

Other aquatic resources in the key waters of the Yangtze River have also recovered. A total of 193 varieties of fish were spotted in the area in the 2022 expedition, an increase of 25 varieties from 2020.

Artificial breeding and release of rare aquatic species have also been carried out to help increase their populations in the wild.

In March, China made a major breakthrough in the protection of the Yangtze sturgeon, an endangered species under first-class national protection, that was declared extinct in the wild by the International Union for Conservation of Nature in July last year.

Natural ovulation and fertilization of the rare fish was observed in a test conducted in a tributary of the Yangtze in Sichuan, signifying that captive-bred sturgeons have the capability to reproduce naturally in the wild.

Moreover, regular monitoring of aquatic species, including plankton, fish, birds and zoobenthos, has been rolled out in China to evaluate the biodiversity of water ecosystems.

"With the help of artificial intelligence (AI), we apply facial recognition to avian diversity monitoring in Beijing," said Liu Bo, head of the water ecological monitoring and evaluation department under the Beijing Hydrology Center.

Last year, an AI-powered monitoring point at Guanting reservoir successfully identified the black-faced spoonbill, a globally endangered waterbird.

China's water quality has also seen notable improvement in recent years as the country shut down highly-polluting factories along rivers and ran environmental impact assessments.

The water quality of the Yellow River's main stream stood at Grade II, the second-highest level in the country's five-tier water quality system, for the first time in 2022, while that of the main stream of the Yangtze River remained at Grade II for three consecutive years.

With clearer rivers and lakes, hydrologists like Guo feel gratified and have more positive expectations for the future. The number of wild fish species in Beijing once dropped to about 40 from 85 due to poor water quality and other reasons. With the improvement of water ecology in recent years, fish species have been gradually recovering.

"In the near future, we may see more fish species revisiting the rivers in Beijing," Guo said.