It's a whale of a tale. Literally.
That's what Randy Thornton, an experienced scuba diver from Draper, Utah, exclusively told ABC News.
Two weeks ago, Thornton and more than 12 friends spent a week diving off the northern coast of the Dominican Republic. They were swimming with and taking pictures of North Atlantic humpback whales that mate and give birth in the waters off the Caribbean island every year at about this time.
"It was a trip we had planned for a couple of years," Thornton said. "We wanted to watch the mating and birthing habits of these magnificent creatures."
Their adventure proceeded without incident until the last hour of the last day. Then it happened.
"The current was pushing the divers into the whale," said Bridget Server, who videotaped the encounter. "They were basically right on top of the whale."
In fact, a group of three divers including Thornton had drifted directly above a 40-ton mother whale and her eight-ton baby, which was sleeping on her back.
From his hospital bed, Thornton explained what happened next.
"They both came up under us. The calf got spooked, spooked the mother," he said. "The mother flipped and threw the group every which way but loose."
The force was so intense, a videotape recording of the accident shows the actual impact and snapping of Thornton's femur, or thigh bone. You can hear a loud pop when his leg is broken.
"It was like getting hit by a train," Thornton said. "You know, it was so hard, it felt like getting hit by car."
Another diver, Janet Blackwelder, suffered broken ribs and was knocked unconscious.
Her daughter Bridget Server photographed the encounter and was devastated.
"She looked dead," Server said. "When I came up from the water, I was screaming 'Mom's dead! Mom's dead!'"
Both injured divers survived, but they then endured a painful nine-and-a-half hour journey back to shore.
"It was a pretty grueling ride," Thornton said. "You can imagine nine-and-a-half hours slamming up and down on a metal deck."
He was then operated on in a primitive 10-foot-by-10-foot cinder-block medical center. He won't soon forget the experience.
"I had an epidural, so I was awake during the three-and-a-half hours of surgery," he said. "They used a hacksaw to cut my bone and hand drill for putting in a rod. Fortunately, the surgery was done fairly skillfully but under such conditions that were beyond belief."
Thornton is now recuperating in Utah, but he's already dreaming of another diving trip.
"It was one of those life changing things," he said. "Absolutely, I'd do it again in a heartbeat."
The message to whale watchers is obvious; don't get too close. Regulations in the United States and Mexico prohibit swimming with whales -- but not so in a handful of countries, including the Dominican Republic, where it's allowed and even promoted.
Whale experts criticize such countries for putting profits ahead of safety.
"It's a double-edged sword," said Bernardo Alps of the American Cetacean Society, the oldest whale preservation organization in the world. "We want and support awareness of whales, but too much of a good thing can be a problem."
In fact, about 90 countries now have whale-watching concessions. The whale tours generate about $1 billion in revenue.
Other whale experts are worried about the impact on the whales, themselves. A study of killer whales by researchers from the University of St. Andrews in Scotland and Dalhousie University in Halifax, Nova Scotia, Canada, revealed that whale watching boats and divers disturbed the animals to such an extent that they decreased their food intake by up to 18 percent.
Conservation groups believe that if whales are frightened away from a good feeding spot by whale-watching activity, they can become weaker and possibly starve.
The Utah divers said they have new found respect for the giant animals.
"It was one of the most incredible experiences of our lives," Thornton said. "The close proximity to these beautiful, highly intelligent animals was great. It was just a weird, freak accident. Like getting hit by a meteorite."
"It's amazing those whales tolerate as much as they do," Alps said. "When you get too close to a humpback whale -- or any whale -- basic instincts take over and they will protect their young."