MONROE COUNTY, Fla. -- The effort to try and rescue more than 40 short finned whales in south Florida will continue Thursday.

But wildlife officials have lowered their expectations, saying more whales might not make it.

"There isn't a whole lot we can do," said Linda Friar, a spokesman for Everglades National Park.

A fishing guide discovered the whales Tuesday in shallow water off the southwestern edge of the park in Monroe County.

Officials have said the location is 20 miles away from the whales' natural habitat.

It's unclear how long the pod of whales has been in the shallow water or exactly what led it there.

Originally, more than 50 whales became stranded, but 10 have died so far.

Six of those were euthanized. The other four died on their own.

According to wildlife officials, euthanasia is sometimes the most humane outcome for whales in this position.

Boats have been in the water trying to corral the mammals into deeper water, but efforts have not been very successful.

Frair said, "We tried this technique called herding, and you can imagine what that is. It's trying to get the boats around them and trying to nudge them out with sound or moving them around. It wasn't effective the first round. Last I heard, they might be trying a second time."

Officials have said more whales might have to be put down. They called Thursday a "pivotal day" for their rescue operations.

A special animal autopsy known as a necropsy will be performed to try and learn more about the whales.

The National Oceanic and Atmospheric Administration said on its Twitter page 1995 was the last time a mass stranding of whales happened in this part of the state.

Short finned pilot whales are protected under law, but are not endangered.

Biologists told NBC News this species of whale is prone to situations like this because they stick together and rarely leave each other behind.

Obstacles like sandbars without a higher tide are making the rescue efforts more complicated.