An orphaned baby dugong rescued in Thailand earlier this year died on Saturday due to pieces of plastic clogging her digestive system, authorities said.

The dugong, whom Thais had fondly taken to calling Marium, meaning "lady of the sea," had been under the care of Thai authorities since she was founded stranded on a beach in the southern Krabi province in April.

They had fed her milk and sea grass, before releasing her back into the ocean a few times, but she came back each time, carrying wounds from her encounters in the sea.

Last week, Marium was found ill, refused to eat and lost a lot of weight, said Nantarika Chansue, one of the vets who took care of the dugong.

She was pronounced dead by the Department of Marine and Coastal Resources on its Facebook page. A team of 10 vets performed an autopsy on Marium, and five hours after her death, they concluded that plastic had killed her.

"Many pieces of small plastic clogged her intestines and caused inflammation, leading to blood infection and inflamed lungs," said Nantarika in a Facebook post.

"Everyone is saddened by this loss, but it reiterates that we need to save the environment to save these rare sea animals."

Dugongs are listed as one of 19 reserved wild animals under Thai laws, which prohibit hunting or trading them.

In June, an association of 10 Southeast Asian countries, including Thailand, adopted a joint declaration to combat marine debris in the region.