LIU CHAN

Tourists take a look at ancient inscriptions on a stone ridge at the Baiheliang Underwater Museum in southwest China's Chongqing Municipality, which opened to the public on May 18, also World Museum Day.

The museum, more than 40 meters under the water surface on the upper reaches of the Yangtze River, protects the world's oldest hydrographic survey device, created about 1,200 years ago to measure changes in water levels of China's longest river.

Baiheliang, literally "White Crane Ridge," is a 1,600-meter-long and 25-meter-wide smooth stone ridge. On it are 20 fish sculptures that served as water-level markers and 165 pieces of inscription left by poets and writers dating from 763 to the early 20th century.

After this precious cultural heritage was submerged because of the construction of the Three Gorges Dam, the Chinese Government invested 189 million yuan ($27.6 million) in building the museum.