The attack happened Monday near pier 14.
A viral Facebook video, posted by Cristy Torres, shows the girl being treated for a bite wound on her leg.
The video has been viewed more than 3 million times.
Torres said she ran over to where the girl had come out of the ocean with her family, which is when she began filming.
The girl was immediately attended to by lifeguards and had the wound wrapped.
"I glanced (in the water) real fast, I saw a tip of a fin," Torres said. "I couldn't tell if it was big or small."
The unidentified girl was taken to a hospital for treatment.
A blacktip reef shark was filmed swimming on June 5 in the same location where the girl was apparently bitten on Monday.
Experts advise against swimming near piers.
ABC News and Stroyful contributed to this post.