Traffic on the southern track of the dual-track ship lock on the Three Gorges Dam resumed on Saturday after a four-month project to raise the lock bed.

Six ships entered the southern track at 8 a.m. on Saturday, marking the reopening of the southern track after raising the beds of its two uppermost tiers from 131 to 139 meters on January 10.

The raising of the lock bed is said to ensure safe navigation for ships when the water level behind the dam finally rises to 175 meters.

"Some 2,000 workers have been working around the clock to get the job done as quickly as possible so that the shipping business on the Three Gorges Dam area would not be affected too much," said Xing Deyong, the commander-in-chief of the Three Gorges Headquarters of Gezhouba Group.

The northern track of the five-tier lock was closed on Saturday for the same operation. The task is expected to be finished on June 30. In the interim, shipping capacity will be down by 60 percent.

The Three Gorges Project, the world's largest water control facility, is located on the middle reaches of the Yangtze River, China's longest and one of the most important inland waterways for shipping in the country. It boasts a 185-meter-high dam, which was completed on June 20, 2006.

The lock, 6.4 km long and costing 6.2 billion yuan (775 million U.S. dollars), was built on mountainous terrain on the northern bank and has been the only navigation route past the dam since 2002.

Construction of the lock began in April 1993. Trial operations began ten years later and it became fully operational in July 2004. By Dec. 31, 2005, about 190,000 ships carrying 89 million tons of cargo and more than 1.88 million passengers had passed through the lock.

Editor: Donald