After getting thousands of suggestions from around the world, they've narrowed it down to two: Fritz or Ferguson.
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You can vote for your favorite name online, at CincinnatiZoo.org.
The winner is expected to be announced next week.
The boy calf was born to 23-year-old Mama Bibi last week and is the birth of a full-term hippopotamus that is a sibling to Fiona, who became a global celebrity when she was born prematurely in 2017.
RELATED: Watch Fiona the hippo grow up at the Cincinnati Zoo
Watch Fiona grow!
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Staff discovered the calf's mother was pregnant around April Fool's Day. It came as a surprise because Bibi was on birth control.
Bibi's first baby, Fiona, only weighed 29 pounds when she was born six weeks premature and wasn't able to stand on her own. Fiona now weighs 2,000 pounds, the zoo said.
The two are staying away from the public for now, but you can check out the zoo's social media for more videos and baby photos.