Nearly 100 pilot whales became stranded on Poinbanka beach in Western Australia on Tuesday. Two days and a near-successful rescue attempt later, they are all dead. 

The long-finned pilot whale pod became stranded on Cheynes Beach earlier this week after they were seen huddling together in a tight group just about 328 feet offshore. Soon after, they had washed ashore for unknown reasons. 

Officials at the Parks and Wildlife Service of Western Australia and hundreds of volunteers went to the beach to try to save the animals – one of the largest dolphin species – but by Wednesday morning, more than half of the roughly 96 whales had died. On Thursday, officials worked to save the 45 pilot whales that remained. 

At first, they seemed to be successful, with volunteers working "tirelessly" to keep the whales submerged as they worked to move them to deeper waters. But within 45 minutes of the attempt to move them deeper, the whales had become "re-stranded further along the beach," the Parks and Wildlife Service said. That's when officials said they had to make a "difficult decision for all involved." 

"Within an hour of beaching, veterinarians had assessed the whales and confirmed they were displaying signs of rapid deterioration," the government service said, adding that two of the whales had already died of natural causes. "Our incident management team then determined the most appropriate and humane course of action was to euthanise the 43 remaining whales to avoid prolonging their suffering."

Mike Conway says he spent more than 9 hours in the water at Cheynes Beach during the "heartbreaking" ordeal. 

"Supporting a 1+ tonne beautiful creature for so long really creates a bond and there were so many emotions we went through, as I'm sure, every volley involved bonded with a mammal (if not the entire pod)," he wrote on Facebook. "Every now and then our whale would take off only to find and nuzzle another whale so we can only assume they were checking in on each other." 

Once it was time to lead them to deeper water, Conway said the team "gave our whales one final rub, wished them luck and pushed them in the direction of the open ocean." 

"We remained in the water, slapping the surface, gently turning a snubby nose around here and there as they turned back the wrong way," he wrote. "...We remained hopeful, but it became evident pretty quickly they were intent on heading back to the shallows. Unfortunately, sometimes nature has other plans, but it's also a testament to these whales extremely close family bonds ."

Incident controller Peter Hartley said in a video statement it "wasn't the outcome we were hoping for." 

"But the one thing I did observe yesterday was the very best of humanity and the best that humanity can offer," he said on Thursday, noting that 350 people were on site to try to help the animals. 

For Conway, the incident has left him "utterly shattered" and "cold to the bone." 

"We will never forget this," he wrote, "and at least we can say we tried our best." 

In:
• Oceans
• Australia
• Whales

Li Cohen

Li Cohen is a social media producer and trending content writer for CBS News.