Workers in central China have fished 78,000 tonnes of debris out of the water at the Three Gorges Dam since October, state media said Sunday.

The clean-up, which began on October 26 when the water level in the dam's reservoir hit its maximum capacity, has involved more than 68,000 workers in nearly 21,000 boats, the official Xinhua news agency reported.

The report cited Wang Yuankai, a Chongqing municipal work administrator, as saying the raised water level made it easier for boats to navigate but also increased the workload for those collecting debris.

It consists mainly of tree trunks, branches and straw, according to previous state media reports.

Household garbage is also a problem, as more than 150 million people live upstream from the dam, and waste is sometimes dumped directly into the Yangtze river because nearby municipalities are unequipped for waste disposal.

China considers the 22 billion-dollar Three Gorges Dam a modern wonder. Since its completion in 2008, it has pumped out much-needed hydroelectricity, increased shipping on the Yangtze and helped reduce flooding.

In August, heavy rains and floods in the area washed a lot of debris into the Yangtze, China's longest waterway, causing concern as it created a pile-up threatening to jam the dam.

It was so thick in parts of the river that people could walk on the surface, state media reported at the time.

Critics charge that the dam has caused ecological damage and increased landslides in the area. About 1.4 million people were displaced by the dam, the construction of which put several heritage sites deep underwater.