(ZHANG XIAOLI)

Workers build a floating dam with oil-absorbing materials near Sanmenxia City in central China's Henan Province on January 5, to prevent diesel-contaminated water from flowing downstream along the Yellow River.

Environmental officials said the diesel that leaked from a ruptured pipeline in upriver Shaanxi Province on December 30, 2009, had been "basically contained" in the Sanmenxia Reservoir on the upper reaches of the Yellow River, China's second longest waterway on which millions of people depend for water supply.

Initial investigations blamed the leakage on a construction accident.