A group of divers made a heartbreaking discovery in Indonesia last weekend, stumbling upon two dugongs imprisoned in a cage on the ocean floor.

Delon Lim told animal rights website The Dodo he found the animals off the remote island of Kokoya.

They appeared to be a mother and her calf held in separate steel cages, the mother tethered with a rope around her tail.

Mr Lim said they had been captured by local fisherman a few weeks ago and kept as an attraction for tourists.

"The ropes are worn and torn. The scars and the wound on her tail are so deep. It was very heartbreaking," Mr Lim said.

He reluctantly paid the fisherman in order to gain access to the cage and document the dugongs' plight.

The fisherman then made an unconvincing pledge to set the animals free, after being confronted over their condition and the fact dugongs are endangered.

Within hours of video of their ordeal being posted online, Mr Lim was contacted by wildlife authorities requesting the location of the cages.

The next day, officials found the animals still trapped.

They were then set free.

Charges will be laid against the fisherman, according to The Inquirer.