A compulsory lightening programme just downstream of the Three Gorges Dam started to have an impact on 12 November when maritime safety authorities in Yichang, Hubei province, ordered 10 coal-carrying vessels to offload some of their cargo before moving downstream to the low waters of the middle reaches.

Officials said that vessels need to have a draught of less than three metres before they can be allowed to pass. The water level has been falling steadily since the start of November and up to 40 vessels carrying coal from Sichuan and Guizhou provinces have been ordered to lighten so far.

In a related development, the Three Gorges Administration has changed right-hand side quayside water marks to red floating buoys downstream of the shiplocks to alert passing vessels of the low water level.