Witnesses say she jumped in the pond on a dare. They say the incident began with a group from the nearby elementary school daring each other to jump off a bridge into a pond.
Emergency crews searched for nearly an hour, finding the girl under the water. They performed CPR on her and then transported her to a nearby hospital where she was pronounced dead.
The girl has been identified as Jordan Oliver.
The park was crowded, but no one was able to was able to go in after her until paramedics arrived.
"There is a sign that says no swimming. What makes you think that today is the date to jump into the pond?" said Crystal Donat, witness.
"I heard a big splash when they jumped in together, and I was looking for the girls," said Jose Ramirez, witness.
According to witnesses, the victim told her friends she couldn't swim and several of them urged her not to jump in.
"I come here to watch the sunset, and it's never going to be the same again, knowing that someone died here and for no reason," said Donna Rudd.
The victim's friends say that she attended Pioneer Elementary School and also lived nearby.