The stricken marine giant was captured in a video taken by divers from the Tiny Dot diving school and posted on Facebook on Saturday.
Tiny Dot reported that the group, led by diving teacher Khru View, spotted the ray during a safety stop while surfacing at the Ko Hin Daeng diving spot in Krabi at 1.08pm on Saturday.
The school said it had asked other divers and the Department of National Parks, Wildlife and Plant Conservation to help locate and free the creature.
The divers spotted that the ray’s right “horn” was entangled in a net about two metres long. No cuts were visible on the manta, which had a wingspan of around 4 metres.
The group were unable to launch a rescue mission immediately as they were low on oxygen. They returned to the boat for fresh tanks, dove back and managed to find the manta ray. However, it was swimming too fast for them to extricate it from the net.
The school said it posted the video to alert other experienced divers to be on the lookout so they could either rescue the ray or alert marine officials to its location.