A pod of killer whales stranded on a beach in southern Queensland, Australia were mostly saved by rescue workers, who enabled five of the seven stranded orca to escape back to sea. However, two whales in the stranded pod died from overheating.

In all, four adults and one juvenile were able to swim back out to sea. A mother orca and its calf died before rescuers were able to save them.

An all-day rescue operation took place Thursday at a sand bar near Stewart Island, about 300 miles (486 km) north of Sydney.

The whales may have been chasing prey when they became stranded on the sandbar in low tide. Killer whales tend to follow the migration patterns of prey such as humpback whales and it is not uncommon for orca to be in the waters this time of year, officials said.

More than one dozen rangers from the Queensland Parks and Wildlife Service responded to the scene, the Australian Broadcasting Company reported.

Windy conditions and the low tide made the rescue operation difficult.