I have been in Laos last days, Luang Prabang. It is really a lovely french town, World Cultural Heritage. During the French Protectorate of Laos (1893–1953) the French have buildt a lot of Daymarks in the Mekong River to prevent the ships from sandbanks! The aim was to achieve a shipping from China to the Mekong Delta ! It never worked!
I have made some pictures. On the larger view you can see the next daymark in the upper right corner! I believe, that these daymarks helps the ships today too! They never have been lighted! I could not find more about these daymarks in the internet! :D