Two toddlers wandered away from their home in northwestern Pennsylvania while their baby sitter slept and accidentally drowned in a nearby pond.

The baby sitter told authorities she put the girls down for a nap Wednesday morning and that she also took a nap. When she woke up, 20-month-old Jenna Walker and 2-year-old Maggie Kovski were missing from the house, the baby sitter said.

She found their bodies floating in a small, man-made fishing pond about 100 yards (90 meters) away from the home and frantically tried to help them.

"She was performing CPR (cardiopulmonary resuscitation), and when I got there, I started CPR on the youngest one," said Chris Barber, chief of Stancliff Hose Co., who was one of the first emergency workers on the scene. "They had no pulse. They were not breathing."

Authorities did not identify the 18-year-old sitter. She was a relative of Walker and lived in the house, which lies in a rural area just south of Erie, Pennsylvania. Kovski was a neighbor's child.

Erie County Coroner Lyell Cook determined the girls drowned and ruled their deaths accidental.

"There's nothing to indicate they were being hurt or drowned purposely or abused in any way," Cook said.

Cook said his ruling would not preclude criminal charges if investigators determined the baby sitter was negligent or reckless. State police Cpl. Mark Zaleski could not estimate when the investigation would be finished.

"This is a very unfortunate, sad, tragic accident for all the families involved, but it still requires us to go through and investigate as we would any other death," Zaleski said.