Elizabeth Lovat was "performing her duties" when the incident occurred on Monday, according to the city's official Twitter account. She was transported to a local hospital, where she remained in stable but serious condition on Thursday.
Details of the incident were not provided.
"Our priority at this time is to provide support for Elizabeth and her family while she recovers," the tweet said. A donation page has been set up by the Huntington Beach Fire Department Outreach Foundation to help cover Lovat's medical expenses.
Authorities said Lovat was not actively involved in a rescue at the time of the incident, the Orange County Register reported.
Lovat is a graduate of Huntington Beach High School, where she graduated with honors.
"Out of respect for the family's privacy, no other information will be provided at this time," the city's statement said.