BEIJING - Water authorities in Central China's Hubei province decided on Wednesday to close the middle reaches of the Yangtze River in response to drought conditions.

On its official website, the Changjiang (Yangtze River) waterway bureau said it was taking that step to prevent ships from bottoming out in the unusually low waters now found between Wuhan city and Chenglingji in Yueyang city. The notice did not say when the waterway will be reopened.

Even though sluice gates in the Three Gorges Dam have been opened partially to allow more water to flow downstream and heavy rains are expected to fall in mid-May, shallow water will continue to impede shipping traffic along the Yangtze River until June, Wu Heping, director of the waterway management department under the Changjiang (Yangtze River) Wuhan waterway bureau, told China Daily.

"The severe drought, the first seen in the past half century, has kept the water level in the Yangtze the lowest since 2003, when the Three Gorges Dam went into operation," Wu said.

"Even though heavy rains are expected in coming months, it's possible they won't raise the water level much along the Yangtze River."

Shallow water in the lower reaches of the river has proved the biggest obstacle to shippers. In Hukou, a city along the river, the water depth fell to 8.41 meters on May 4, a historic low, according to statistics from the Changjiang (Yangtze River) waterway bureau.

He said the waterway is about 150 meters wide on average, which is 50 meters narrower than it was in 2010.

Because of the low water, at least two ships have been stranded within the past two days and dozens of emergency teams have been sent to the river's middle reaches to prevent accidents, according to the bureau.

Maritime safety bureaus in Chongqing, Wuhan and Huangshi last week issued alerts and offered help to ships that had run aground.

Since April 30, more than 700 ships have been stranded in the narrowed waterway in Huzhou, Xinhua News Agency reported on Thursday.

The 6,300-kilometer Yangtze River is the country's longest waterway and is indispensable to the economies of cities lying along its route.

The river's water level has fallen sharply since February 2011. In the past five decades, the level in its middle reaches has dropped to a historic low point and the water depth near the Three Gorges Dam has been at a historic low since 2003.

To mitigate the harm inflicted by the drought, the dam's rate of discharging water was increased from 7,000 cubic meters a second - what it was on Saturday - to 9,220 cu m per second at 2 pm on Monday. The new rate means the dam lets out 3,020 cu m more water each second than it takes in, according to the latest statistics released on the official website of the China Three Gorges Corporation.

The water depth at the dam has fallen below 155 meters, a level that threatens to make generating power difficult. The depth stood at 154.76 meters at 3 pm on Monday, according to official statistics.

Some experts blamed the low water along the Yangtze River on the Three Gorges Dam.

Wang Jingquan, director of the flood control and drought relief office affiliated with the Yangtze River Water Resources Committee, told China Daily on Monday that damming up the river has aggravated the drought by pinching off water flow to lower reaches.

Yan Fei, director of the China Three Gorges Corporation's press office, said such assertions are groundless. He said statistics show the dam's increased discharge of water has helped to relieve the drought.

From Saturday to Wednesday morning, the Three Gorges Dam discharged about 4 hundred million cu m of water, lowering the water level of the dam by 0.7 meters, said Wang Hai of the dam's construction and operation management bureau.

About 400,000 people in the province are without drinking water as a result of the drought, and approximately 870,000 hectares of farmland have been harmed by it, according to the Hubei provincial agricultural department.