Peace officer Jamie Brown was on the rescue boat that capsized Sunday in Lake Newell. (CBC)

A veteran peace officer who was on a rescue boat that capsized in a southern Alberta lake, killing a five-year-old girl, said high waves left them all scrambling to survive.

Jamie Brown, a peace officer with 20 years experience, as well as an RCMP officer and a Fish and Wildlife conservation officer, were responding to a call for help from a family that was boating on Lake Newell, near the city of Brooks.

The RCMP said the family of five from the Calgary area was boating late Saturday afternoon when their vessel hit a rock. They called 911 for help.

Two hours later, a 5.5-metre rescue boat from the Fish and Wildlife Department located the family and headed for safety.

Lake Newell, near Brooks, on a calm summer day. (Submitted by Christine Ring)

It was extremely windy and waves were reaching heights of more than 1.5 metres at times, said RCMP Const. Francine Hiebert.

"It just got to the point where we couldn't recover from the amount of water coming in and it swamped," said Brown Monday from his hospital bed.

The rescue boat capsized, throwing its eight occupants into the water.

"Couple times I gave up, you know just got exhausted," said Brown. "I was treading water. It seemed like I was just going in circles, the waves were too big."

Emergency crews on shore lost contact with the rescuers until a police helicopter located the boat at 11:25 p.m. Some were in the water and some were clinging to the top of the overturned rescue boat, said Hiebert.

The little girl was eventually found trapped under the vessel early Sunday after it was towed to shore.

Her parents and two siblings, along with the three rescuers, were suffering from hypothermia.

All members of the family were wearing life jackets during the entire ordeal, the RCMP said.

The family has asked police not to release the girl's name to the media.