Plateau lakes in the wild habitat of the critically endangered Tibetan antelope are swelling with flood water that may disrupt the animals' forthcoming migration and birthing season.

Khuse Lake in the Hoh Xil nature reserve of northwest China's Qinghai province has swollen with flood water since last September and has overflown into the Haiding Nor and several other lakes, said Xiao Penghu, deputy chief of the Hoh Xil nature reserve administration, on Thursday.

The swelling lakes and the flood water have inundated the routes of Hoh Xil mountain patrollers, who have to search for alternative paths.

Patroller Karma Yarphel said a river on his route to Khuse Lake had grown from 80 meters to about 600 meters wide. "I've never seen the river swelling like this before," he said.

The reserve administration is watching the swelling lakes closely, as flood water has also inundated the migration routes of Tibetan antelopes.

Pregnant antelopes migrate to the Hoh Xil reserve, known as the species' "delivery room," every June to give birth, and leave with their cubs in September.

The migration covers about 530,000 square kilometers.

"The earliest group might start migrating at the end of this month," according to Xiao.

Kang Aili, a project officer with Wildlife Conservation Society, said it was hard to tell immediately how the excess water may affect antelopes' migration.

But she warned, "They will need to change their route and adapt to the new routes fast enough for the species to sustain."

Tibetan antelopes, mostly found in Tibet, Qinghai province and the western part of Xinjiang Uygur autonomous region, are critically endangered and under first-class state protection in China.

There used to be millions of them on the Qinghai-Tibet Plateau, but excessive hunting and human encroachment on their habitat caused their population to plummet in past decades.

Poachers hunt the antelopes for their hide as it can be sold and made into shahtoosh shawls, with each of these luxury items requiring three to five antelope skins.

Since 1979, the animal has been recognized as an endangered species and protected under the Convention on the International Trade in Endangered Species.

Chinese conservation officers launched a campaign to crack down on illegal poaching of Tibetan antelopes in 1999 in Hoh Xil, a reserve that encompasses China's largest area of uninhabited land.

The reserve has about 70,000 antelopes now.

Authorities are baffled as to the cause of the flooding. "Meteorological records provided by the local weather bureau showed no significant rise in rainwater since last fall," Xiao noted.

Melting glaciers on the Qinghai-Tibet Plateau could be a reason, but even the glacial water cannot explain such a flood, he explained.

Glaciers on southwest China's Qinghai-Tibetan Plateau, the source of China's largest rivers, are melting faster than ever before under the impact of global warming, researchers have found.

About 82 percent of glacial surfaces on the plateau have retreated, and the glacier area has decreased by 4.5 percent in the past 20 years, data from the China Meteorological Administration has shown.

"We need to step up dynamic surveillance and carry out geographical, hydrological and meteorological researches to find out the cause of the floods and their potential impact on the plateau ecology," said Xiao.