An adorable baby Pygmy Hippo just marked an important milestone as he first splashed and swam in the water at Melbourne Zoo while his mother Petre watched him.

The name Obi means "heart" in Igbo, a local Nigerian language. The calf had grown quickly, putting on around 500 grams a day. He was born around 5 kilos but is now 13 kilos.

And yes, this calf is growing and learning to swim in a small pool with the help of his mother, but it turns out he is a natural swimmer and loves the water, BBC News reported.

"He loves the water and spends hours in the small pool, so he is ready for the next step," Wild Sea Manager Justin Valentine said.

Obi and Petre can be seen in the zoo but would not be on display all the time because Obi would need to rest.

Four-week-old Obi was born on May 25, and he is the first of his species to be born at the Melbourne Zoo since 1981, The Guardian reported.

Pygmy Hippos are considered to be endangered in the wild, but their exact population size is unknown because of their dense rainforest habitat.