The argument that hydropower construction may contribute more pollution than thermal power plants has stirred controversy among the country's top authorities, reported Chinese media on Sunday.

Ling Jiang, deputy director of the department of pollution prevention and control under the Ministry of Environmental Protection said recently that hydropower was not as clean as people thought and might cause more pollution than thermal power, said a report by China National Radio.

He said the development of hydropower projects destroyed parts of the ecosystem and caused water and soil erosion in nearby rivers.

The argument immediately triggered a stir among senior officials and hydropower experts.

Zhang Baoguo, director of the National Energy Administration, said reservoirs are not the reason for worsening water quality in nearby rivers.

For instance, Zhejiang province's Qiandao Lake, an artificial lake caused by the Xin'anjiang Hydropower Station built in 1959, has turned the surrounding landscape greener and attracted many tourists. Likewise, the Ertan Hydropower Station in Sichuan province, completed in 2000, has become a prominent tourist resort, he added.

Han Xiaoping, chief information officer of domestic energy portal china5e.com, said any energy will damage the environment and hydropower, as an important relatively clean energy, should be given priority in energy development in China.

Thermal power has taken too large a share in the country's energy production, with annual coal consumption reaching nearly 70 percent of total energy consumption and it is expected to reach 4 billion tons in 2015, Han said.

He added that thermal power production will not only produce greenhouse gases, but would also discharge a great amount of nitrogen oxides and dust containing heavy metals that are harmful to health.

Mao Xianqiang, professor of the School of Environment at the Beijing Normal University, told China News Service on Monday that, generally speaking, hydropower was categorized as clean energy because of its small pollutant emissions, but it also affected ecosystems due to the changes it caused in geological conditions, such as cutting off the water flows and submerging land.

Disputes over the effects of hydropower stations have long existed as hydropower may become an important energy source in the future.

In August, Zhang said China has 400 million kilowatts of potential economically usable hydropower and the country is expected to expand its installed hydropower capacity to 300 million kilowatts by 2015 in an effort to cut carbon emissions.

The country's 12th Five-Year Plan (2011-2015) has also noted the country's ambitions in hydropower development.

China approved several new hydropower projects in 2010 to speed up its development of clean energy, with the National Development and Reform Commission approving the construction of Changheba hydropower project, Guandi Hydropower Station and Tongzilin hydropower project in Sichuan province, Wudongde and Baihetan hydropower projects in Yunnan province.

Work on Zangmu Hydropower Station in the Tibet autonomous region, the world's highest, started on Sept 27, 2010. It will have a capacity of 510,000 kW. The station is expected to ease power shortages in central Tibet and boost regional economic development.