A zoo in Belgium has shared some amazing photos of a blossoming friendship between a family of orangutans and their otter neighbours.

The animals live together at Pairi Daiza zoo in Domaine du Cambron, as part of a program designed to maintain the primates' wellbeing in captivity.

According to zoo spokesman Mathieu Goedefroy, they "must be entertained, occupied, challenged and kept busy mentally, emotionally and physically at all times."

As part of the program, the family of Asian small-clawed otters were allowed to live in the river that runs through the enclosure that houses the orangutan family: 24-year-old father Ujian, 15-year-old mother Sari and Berani, their three-year-old son.

"The otters really enjoy getting out of the water on the orangutan island to go and play with their big, furry friends," said Goedefroy, adding that Berani and Ujian have developed a particularly strong bond with their neighbours.

"It makes life more fun and interesting for both animal species, which makes it a very successful experiment," he said.

The orangutan family arrived at the zoo in 2017. Another two orangutans also live there: Gempa, a male, and Sinta, a female.

Orangutans share 97% of their DNA with humans and as a result require a lot of attention to keep them occupied, Goedefroy said.

"Our keepers entertain them all day long with mind games, riddles, puzzles, and other stuff to train their intelligence," he added.

Orangutan populations are threatened by palm oil plantations in their native Borneo and Sumatra. Goedefroy told CNN that the zoo has raised funds to plant 11,000 trees to restore a forest in Borneo.