The biggest hydropower plant in the environmentally vulnerable province of Yunnan released about 2 million fingerlings into a reservoir on Friday in Pu'er city.

The move was part of a series of fish releases in lakes and reservoirs on the plateau intended to maintain biodiversity and help clean the waters.

The Nuozhadu plant spent 3.85 million yuan ($620,000) to buy 6.35 million fish, including 350,000 indigenous fish. On Friday, about 10 officials from the Pu'er city government attended the fish-release ceremony and put 2.15 million fish into the reservoir.

Yunnan, known for its natural beauty as one of the top tourism destinations in China, also has a fragile ecology, which will take a long time to recover if damaged.

Experts said the fish releases, though seemingly just a small step, were positive for maintaining the natural environment.

The release was another step to keep the commitment to maintaining the biodiversity of areas surrounding the reservoir, said Wang Ziwei, the plant's manager, at the ceremony.

An annual fish release was also carried out last week to put 7 million fish into Dianchi Lake, a polluted body of water in the provincial capital Kunming, to help purify the water, local authorities said.

Located about 40 kilometers from downtown Pu'er, the Nuozhadu Reservoir is equal to 16 Dianchi Lakes, with a designed restoration of 23.7 billion cubic meters of water.

Owned by China Huaneng Group, the Nuozhadu dam is 261 meters high, making the plant the biggest of eight hydropower plants on the Lancang River, a major river in Yunnan. The river is known as the Mekong in Southeast Asia.

"Hydropower plants often arouse controversy about their ecological impact, so our plant keeps a close eye on the environmental impact in addition to the economic output," Wang said.

"Therefore, we are trying to maintain a good ecosystem in the reservoir so that people nearby can also benefit from the project."

Since the start of construction, the plant has paid attention to environmental issues and biodiversity protection.

"Usually, hydropower reservoirs drain water from the bottom that will easily lower the temperature of the downstream water and threaten living conditions for fish and other species.

"Therefore, we invested an additional 200 million yuan to build the dam so that it can simultaneously drain some water from the bottom and some from above to raise the water temperature, which will be helpful to fish downstream," Wang said.

Ouyang Xibin, director of the security and environmental protection department at the plant, said the fish will mature in five years and bring at least 1.5 billion yuan of revenue for local residents, who are allowed to fish in the reservoir.

Two years ago, Huaneng Group established a rescue station for endangered animals, the first sponsored by a company in China. So far, the station has provided shelter for 102 injured animals such as lorises, crocodiles, monitor lizards and black bears.

At the station, a dozen monkeys were playing or fighting in iron cages on Friday and the breeders said all the animals will be released into the wild when their injuries have healed.

Li Yingqing and Guo Anfei in Kunming contributed to this story.