POYANG, China (AFP) — Spooked by a historic drought, local authorities in China have renewed controversial plans to dam the country's biggest freshwater lake.

But environmentalists warn damming Poyang Lake, a winter stopover for over half a million birds, would threaten the fragile ecosystem and the endangered birds and other wildlife it supports.

The Poyang dam, which is slowly recovering after shrinking to less than a third of its usual size, shows how fraught such efforts are in China.

Conservationist Zhang Daqian said that if realized, the 3,000-meter-long sluice gate across one of the lake's channels would cut it off from the river Yangtze, "leaving Poyang a dead lake."

Poyang supplies water to Jiangxi province's 4.8 million residents, and the local government says damming it will conserve water, irrigate more farmland and improve navigation.

Its mud flats are the primary winter feeding grounds for hundreds of thousands of birds flying south to escape the chill every autumn.

They include the critically endangered Siberian crane, the population of which has shrunk to about 4,000.

"Migratory birds are still coming to Poyang, because it's their habitual winter home," an employee surnamed Chen said, looking across the dry expanse littered with empty mussel shells and fish skeletons.

Food chain disruption

It's not clear what stage of development the dam is currently in, and neither local authorities nor the environment ministry responded to questions put to them by AFP.

But were they to go ahead, the sluice gate would disrupt the lake's natural ebb and flow with the Yangtze, potentially threatening the tidal flats the birds feed on, Lu Xixi, a geography professor at the National University of Singapore, said.

Losing its natural water circulation could also hurt Poyang's ability to flush out nutrients, risking an algae build-up that could disrupt the food chain, Lu added.