The zoo said the calf was born in the water at the hippopotamus compound. It took about two hours. Officials don't know yet whether it's a male or a female - the calf is staying close to its mother.
The hippo has not yet been named. It was born to a female named Funani and a male named Otis. Otis was brought to San Diego from the Los Angeles Zoo two years ago.
The zoo says the two didn't get along for awhile but they began to mate in April.
The Associated Press contributed to this story.