Jeff Harris was on a beach in The Outer Banks, N.C., with friends, kicking a soccer ball in the surf. Diving for the ball in shallow water, he hit his head on the sand with such force that he couldn't move. He kept trying to lift his head but it became so tiring that he just let it dangle in the surf. He eventually passed out.

A nurse sitting on the beach nearby administered CPR, even after she was told to give up because he had no pulse. She revived him, however, and he was airlifted to a nearby hospital where he learned he had fractured his sixth vertebra. Harris, 30, is now paralyzed from the neck down. "That nurse was just hanging out with her family and said she was taking pictures of me because she thought I looked hot, running around on the beach," Harris says. "She may actually have one of the last pictures of me as a walking person."

Harris is not alone. Jesse Billauer, 34, was surfing in Malibu, Calif., riding a wave into one-meter-deep water when he was thrown into a sandbar, severing his spinal cord. Chad de Satnick, 36, was riding a wave in Cape May, N.J., when he hit shallow water, flew off his board and into the sand, fracturing his sixth and seventh vertebrae. Patrick Durkin, 59, was body surfing in Ocean City, Md., when he was caught unexpectedly by a wave close to shore. He rode it in but was thrown into a wall of sand that broke his neck. The list of bathers with spinal injuries goes on.

Although no one seems to know why so many people are injuring themselves in the water, researchers in Delaware are at least trying to figure out when—that is, are there times when it's more likely to happen? Perhaps when the wind is blowing in a certain direction or the waves are a certain height. If they can predict when these injuries are more likely to occur, they can warn people about going into the water.

Paul Cowan, who heads up the emergency room at Beebe Medical Center in Lewes, Del., decided to study the issue after noticing that surf-related injuries came into his emergency room in waves. On some days there would be no surf injuries whereas on others there would be 12 or 13. The largest number was 25 in one day. "It was the episodic nature of the injuries that caught my attention," Cowan explains. "I always wondered, what's different on that day than the day before or after?"

He wanted to know if there was something going on with the water that caused these precipitous spikes. He teamed up with researchers at the University of Delaware, and for three years they have been collecting data on the number of surf injuries on five beaches in the state, comparing it with specific environmental factors such as air and water temperature; wind speed and direction; and the height, angle and period of waves; to see if a pattern of injury occurrence emerges.

To date they have tallied 1,100 spinal injuries. Although most were more minor, such as 400 dislocated shoulders, there were also three fatalities. And 55 of the total were cervical fractures, some of which may have resulted in paralysis. (They don't track people after they've left the emergency room.) Surf-related spinal injuries are not that rare, Cowan says. "One of my first observations when I came here 11 years ago was that in car accidents you look for spinal cord injuries—and they're not very common. Here, I saw a lot of people injured in the surf who actually had cervical injuries," he notes.

As Cowan and his group search the sea and the sky for clues about why people are getting injured, some believe they already have answer, and they're pointing down—to the sand. Surfers and lifeguards blame many of the surf-related injuries—particularly those affecting the spine—on beach replenishment, the process by which new sand is pumped on to beaches to protect the coastline from storms and erosion. They say adding new sand doesn't just make beaches wider, it makes them higher, resulting in steep slopes that can cause large waves to break close to shore. "We never really had spinal cord injuries until beach replenishment. There is a direct correlation," says Jerry Inderwies, Cape May's fire chief, adding, "There's been a significant increase in all kinds of surf-related injuries, from dislocated shoulders to abrasions, head wounds and contusions."

Replenishment also eliminates sandbars that would normally reduce wave energy farther offshore, says John Weber, mid-Atlantic regional manager for Surfrider Foundation, an environmental group. Between the steeper slopes and fewer sandbars some of the waves breaking near shore are packing a heavier punch. "A beach that is replenished is potentially more dangerous than a natural beach," Weber adds.

There have been no studies to date on the link between beach replenishment and spinal injuries, but when one looks at some of the beaches that have undergone replenishment (aka “renourishment”) projects, there is often a spike in "major medical" injuries—or those requiring emergency medical services—that same year or the following year, according to data reported to the United States Lifesaving Association (USLA).

Take Ocean City, which the U.S. Army Corps of Engineers says was replenished in 2006. There were 87 major medical injuries that summer, according to USLA data. The following year there were 345. After a second replenishment project in 2010 injuries rose from 233 to 306 the following year. In Cape May, which the Corps confirms was replenished in 2007, injuries rose from 12 that year to 35 in 2008, according to the USLA. After a second replenishment in 2009 injuries rose from 35 in 2008 to 41 that summer and reached the same total in 2010. Following a third replenishment in 2012 injuries rose from 15 in 2011 to 45 that year.

Cape May's numbers were so high in 2008 that the late Sen. Frank Lautenberg (D–N.J.) asked the Corps to investigate a potential correlation between spinal injuries and beach replenishment. The Army never completed the study because they said they don't need to—they did not believe there was a link. "We don't have any data showing us a correlation or relationship between beach nourishment and spinal injuries," says Edward Voigt, chief of public and legislative affairs in the Corps's Philadelphia office. "If someone had information like that—not anecdotal but some kind of data or analysis, with actual facts associated with it—that would give us something to look at."

Whereas Voigt acknowledges beach replenishment can result in steep drop-offs near the shore, they don't necessarily result in injuries, he says. "There are so many factors that come into play with injuries: Was it high tide? Low tide? What time of year was it? Were there storms? Was there an increased use of the beach? A lot of things can affect injuries," he notes.

Indeed, that's exactly what Cowan and his team are trying to figure out. So far, their research has yielded a few discoveries: Most injuries occurred on days when the waves were 0.45 to 0.75 meters high. And those hurt were often bathers—not surfers—standing in less than knee-deep water with their backs to the ocean when they were suddenly knocked down by a wave and slammed into the sand. "We want to create an algorithm using a series of environmental factors so that we can predict in real time whether it's more dangerous to go in the water," Cowan says.

The idea is compelling enough that when Cowan spoke at a conference recently, representatives from the National Weather Service approached him to see if they could join forces to come up with a "surf zone injury" forecast, not unlike a weather forecast.

What Cowan's research has not conclusively determined is whether spinal injuries are the result of beach replenishment. "Everyone has an opinion about why they're happening," Cowan says. "I'm not able to say why."