At Khao Kheow Open Zoo, just outside Bangkok, crowds gathered as the birthday girl was treated to a colourful cake made entirely of fruit and vegetables.
Moo Deng was slow to join the party, preferring a splash in the water – until her mum Jona took the first bite.
Fans flew in from as far as the US, some making their second or third visit to see the playful hippo.
Since her birth, Moo Deng has gained thousands of online followers, drawn to her bouncy antics and cuddly charm.
The zoo says auctions of her photos, footprints and even her food tub are helping raise funds to support its animals.
The pygmy hippopotamus is native to West Africa, where it's threatened by poaching and loss of habitat. There are only 2,000-3,000 of them left in the wild.
