Almost one month after an earthquake devastated Yushu County, in northwest China's Qinghai Province, local residents and officials are still removing animal carcasses and pollutant trash from the area to prevent ecological damage and the tainting of water supplies.

As reconstruction work began lately, local officials told Xinhua the quake had not damaged the water and soil in the Sanjiangyuan region, the source of China's three major rivers: the Yangtze, Yellow and Lanchang rivers.

Yushu lies in the heart of the Sanjiangyuan region, nicknamed "China's water tower," and sits at an average altitude of more than 4,000 meters.

"The vegetation, the biodiversity and the ecosystem in Yushu remained intact after the quake," said Ren Jie, an official with the provincial environmental protection department.

Officials with the local animal epidemic prevention and monitoring center have kept a close watch since the quake, on the lookout to prevent pollutants released by the quake from entering waterways and threatening Sanjiangyuan's ecology.

Some 20,000 leaflets in Tibetan and Chinese were distributed to urge local residents to report any animal carcasses. As of April 30, nearly 43,000 sheep, cattle, dog and horse carcasses had been disposed of in a biologically safe way, local authorities said.

Two open fields far from water reservoirs were chosen as sites for the burial of quake rubble and garbage.

After animal plagues, glacier shrinkage and grassland degradation began to affect Sanjiangyuan in the 1970s, the government launched a 7.5-billion-yuan (1.1 billion U.S. dollars) project to preserve the region's ecology in 2005. It was and remains China's largest ever ecological conservation project.

From 2005 to 2010, more than 20,000 Tibetan herdsmen in Yushu migrated off the grasslands to protect the environment.

But they suffered huge losses in the quake, and they may return to pastures in Sanjiangyuan, according to Zhao Niannong, vice director of Qinghai's agriculture and animal husbandry department.

The 7.1-magnitude earthquake on April 14 left at least 2,200 people dead and more than 100,000 homeless.

"Problems concerning their livelihood must be solved quickly, otherwise all the efforts to preserve the ecology over the past few years will come to nothing," Zhao said.

Local officials also urged a large number of quake-resistant greenhouses with good heat preservation functions be built as part of the reconstruction program. They will supply vegetables and double land-production efficiency in the high-altitude area.

In Yushu, about 1,920 of the 2,270 greenhouses were damaged in the quake.

"One clear-cut principle in the rebuilding of Yushu is to fully preserve the local environment. The rebuilding plans and funds will also help preserve Sanjiangyuan's ecology," Zhao added.