Bangkok Metropolitan Administration (BMA) is asking city residents to go "zero-foam" for this year's Loy Krathong festival and urging use of biodegradable floats to help protect the environment.

The deputy director of City Hall's Environment Department, Worranut Suaykhakhao, said despite previous pleas to go foam-free, about 20,877 out of the 639,828 floats collected by BMA's waste collection units after last year's Loy Krathong festival were made from foam.

This year, Ms Worranut said, BMA wants to see fewer floats made out of foam, saying the krathong used should be made from 100% natural, biodegradable materials that wouldn't harm the environment as they break down.

Bread floats, for instance, will naturally break down, but they will raise the acidity of the water as they begin to decompose, potentially harming aquatic life, especially in bodies of water that are stagnant.

Last year, she said, the Department of Drainage and Sewerage had to drain the fish pond in Suan Santiphap Park -- where residents released 6,800 bread krathong -- as the decomposing floats polluted the water, killing off the fish.

It took the department four months to bring the pond back to its original state, she said.

The department is also urging krathong vendors to refrain from using metals in the floats, as these have to be sorted out before the floats can be properly disposed.