A black, odorous body of water that used to be dotted with dead fish in the Inner Mongolia autonomous region has been rejuvenated and is now a paradise for birds thanks to local authorities' conservation efforts.

Photographer Qi Hongyan still has vivid memories of a visit to Ulansuhai Nur, the biggest lake in the Yellow River basin, almost a decade ago.

"When the boat I was on cruised across the lake, the propeller stirred up black water," he said. "I tried to make the water not look so black in my photo by adjusting the camera's exposure, but I couldn't."

A bad smell engulfed the air, and you could easily find dead fish floating around the lake's shore, he added.

According to local authorities, the lake's environment deteriorated due to years of pollution from agricultural, industrial and domestic waste water, with inadequate replenishment of the lake water from the Yellow River making the situation even grimmer.

But when Qi, 64, recently revisited the lake in Urad Front Banner, Bayannuur League, what he saw left him stunned.

"The water was so beautiful. It is azure blue in the photos," he said.

As the boat moved, a school of fish closely followed, and big flocks of birds came into sight now and then. "I was so excited," he said.

Zhang Zhijia is more keenly aware of the change in the lake as a resident of Wayaotan village, which lies near it.

Villagers suffered a lot from the lake's terrible environment. Its black, odorous water offered favorable conditions for mosquitoes. It was no exaggeration to say that a random pat on your face could kill several insects when you walked near the water, he said.

But thanks to the improvement of the lake's water quality, there has been a sharp decrease in the number of mosquitoes, Zhang said. In stark contrast, the number of birds has risen noticeably.

Zhang, 52, said he remembers white swans showing up at the lake in "twos and threes" before the water quality turned bad. Currently, however, they arrive in flocks.

The protection of the Ulansuhai Nur basin has been a matter of concern for President Xi Jinping.

While deliberating with fellow deputies from Inner Mongolia at the fourth session of the 13th National People's Congress on March 5, Xi said he had issued directives about the lake multiple times.

There has been marked improvement in the area, but persistent efforts are still needed, he stressed.

According to local authorities, over 260 bird species either live at the lake or rest there as they migrate. Their number totals 6 million, but no previous figures are available for comparison because of a lack of observation.

Du Zhangui, director of the Ulansuhai Nur ecosystem protection center, said that all the water in the lake was previously below Grade V, the lowest in the country's water quality system.

Now, some of the parameters for water quality assessment in some parts of the lake have reached as high as Grade II, the second-highest level, he added.

According to local authorities, aside from beefing up fertilizer and pesticide control at nearby farms, 11 sewage treatment plants have been built in the area as part of the local government's efforts to prevent pollutants from entering the lake. A 60-square-kilometer wetland has also been created to help purify water before it enters Ulansuhai Nur.

The local government has also been diverting water from the Yellow River during the flood season to supplement the water body.

However, Zhang said the water quality is still far from what it was when he was young.

"You could drink water from it directly back then," he said.

Most of the funding to conserve the water body comes from higher levels of government, but as water quality keeps improving, he expects to see tourists flock to the lake and bring the area revenue that could be used to make the local environment even better.