The festival is usually a time when millions of Thais celebrate the end of the so-called rainy season by floating small rafts decorated with candles, incense and flowers.
But the mood in the Thai capital Bangkok was sombre on Monday as mourners marked the end of the first month of one year of official mourning for the king, who died on Oct. 13.
King Bhumibol was seen by many Thais as a stabilising force through an era of rapid change and social upheaval in the Southeast Asian nation.
"We have asked for celebrations to be muted this year because this is a sensitive time for the country," Patarut Dardarananda, permanent secretary at the Bangkok Metropolitan Administration, told Reuters.
"City hall has asked that people not set off fireworks and firecrackers to respect the mourning period."
At Bangkoks famed Lumpini Park, vendors selling the floating baskets were scarce.
"This year is not like most years, we have to be respectful," said vendor Kwanjai Weelai.
The festival is normally a time when Thailands rivers, lakes and seas are filled with glittering candle-lit floats. It is said to originate from an ancient ritual that paid respects to the water spirits.
Some festival-goers also believe that adding nail clippings or locks of hair to the floats will help to get rid of bad luck.