On Wednesday, many people, including monks, showed up at the banks of the Chao Phraya to perform rites to mark Visakha Bucha Day and release buckets of catfish.
However, most of the fish died because their bodies hit the stairs leading to the river or they could not adapt themselves to freshwater.
Thais, especially devout Buddhists, believe that releasing fish earns them merit, but many environmental organisations are warning that releasing wrong fish in unsuitable water bodies may have a severe impact on the ecosystem.
Visakha Bucha is one of the most important holidays in the Buddhist calendar, as it marks Buddha’s birth, enlightenment and death.