Undated file photo shows two researchers working on the Zhongbao Island on the Yangtze River in Yichang, central China's Hubei Province. The Zhongbao Island has submerged in the 2,309-meter-long and 185-meter-tall Three Gorges Dam, whose construction was started on July 1, 1994 with the island at its core. [Xinhua Photo]

Undated file photo shows the Zhongbao Island in the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]

The file photo taken in October 1997 shows the Zhongbao Island in the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]

Undated file photo shows a construction site on the Zhongbao Island in the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]

Photo taken in May 2006 shows the Three Gorges Dam, whose construction is close to end, on the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]

Tourists take an overlook of the Three Gorges Dam under construction on the Yangtze River in Yichang, central China's Hubei Province, in May 2004. [Xinhua Photo]

Photo taken in November 2001 shows the left side of the Three Gorges Dam under construction on the Zhongbao Island in the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]

The file photo taken in October 1997 shows the Zhongbao Island in the Yangtze River in Yichang, central China's Hubei Province. [Xinhua Photo]