The dried-up bottom of Dongting Lake is seen near Yueyang fishing harbor in Central China's Hunan province yesterday. [Xinhua]

Dongting Lake, the nation's second largest freshwater lake, has decreased by more than 90 percent compared with its average capacity during the flood season, a local official said.

Presently the lake's total volume is about 770 million cu m, less than 10 percent of the average volume during the flood season, said Jiang Yimin, director of Hunan provincial environmental protection bureau, to the Economic Information Daily yesterday.

The lake is located in the middle reaches of the Yangtze River.

Successive years of drought in the upstream areas have led to the lake's low volume, it reported.

Water levels at the Songzi, Hudu and Ouchi rivers, three tributaries of the Yangtze River, have dropped since 1974.

The lake's water area, which spans Central China's Hubei and Hunan provinces, measured about 538 sq km in mid-October, only 40 percent of its capacity in September, Xinhua reported.

The operation of the Three Gorges reservoir has exacerbated the drought, leading to a decrease in water flow into the lake, the newspaper quoted anonymous experts as saying.

In the 1950s, about 150 billion cubic meters of water flowed from the Yangtze River into Dongting Lake each year. From 1990 to 1998, the annual flow into the lake was lowered to 88 billion cu m. Water flow into the lake was merely 1.53 billion cu m from September to October in 2006, the report said.

The lake's water volume dropped again after the project on the Three Gorges reservoir began to raise the reservoir's water level since mid-September.

The water level at the reservoir had been scheduled to reach its peak of 175 m by the end of October but the original plan was postponed due to the severe drought that struck the vast areas in the middle and lower reaches of the Yangtze River.

The drought has caused wetland areas to shrink around Dongting Lake, reducing the lake's self-cleaning capacity. It has also affected local agricultural production and drinking water safety.

China has more than 24,800 natural lakes, but they are disappearing at a rate of about 20 every year, Xinhua reported this month.