Last month I was fortunate enough to be in Laos for Boun Ok Pansa. Here is a description I found from another website.
Held to celebrate the end of Buddhist Lent, the nationwide Ok Pansa Festival starts at dawn on the first day with donations and offerings made at wats around the city. Then in the evening candlelight processions are held at wats, and in a ceremony known as boun lay heua fai (equivalent to loi krathong which the Thai people celebrate in December) hundreds of colourful paper boats decorated with flowers, incense and candles are set adrift on the Mekong River to pay respect to the river spirit and eradicate bad luck, bad deeds and disease.
I originally didn't want to go as I was in sort of a funk, but ended up checking out the parade and had a wonderful evening. Each village builds lavish boats, usually with naga (river dragons) themes. The boats are judged and a village is crowned winner, enjoying the street-cred that comes with it. Candles are everywhere as is the spirit of merriment. I ran into a friend from a different village and walked in the parade with him and his son alongside other villagers of his and their boat. Near the end his son got tired and I had to carry him all over. Needless to say, carrying kids is tiring. :)
After the judging, the boats are put in the water to float away. People also offer up little boats made from banana leaves with incense and candles. The city is ablaze with lights and good feelings. Paper lanterns are also offered up to the heavens.