The girl, who has not been named, was jet skiing with her friends when she spotted a pod of dolphins and tried to swim with them, ABC News (Australia) reported. Instead, she found a shark that bit into her leg.

Witnesses say a young man jumped in to retrieve the girl, with many describing him as a hero. One witness suggested the young man could have been the girl’s boyfriend.

Paramedics rushed to the scene but were unable to save the girl, who suffered significant injuries to her leg. Both the shark’s species and the full nature of the girl’s injuries remain unreported.

This is the first death in the river for a century, with the only other confirmed fatal attack occurring on Jan. 31, 1923.

"It's an extremely traumatic event for everyone involved and everyone who knew the young girl, so I won't be going into the extent of the injuries," Fremantle District Acting Inspector Paul Robinson said, describing the incident as "tragic."

"It is unusual for a shark to be that far down the river," he continued. "At this point in time an alert has been put out, a shark warning just to let people know this incident has taken place."

Robinson also noted that the girl’s family were reportedly not present at the time, but have since been informed and are "absolutely devastated."

"However her friends were and as you can imagine this is an extremely traumatic incident for anyone to witness so obviously, we’re offering counseling services to anyone who did witness it or is affected by the incident," he said.

Authorities urged the public to "take additional caution in the Swan River in the North Fremantle area," according to News.com.au.