In 1988, Marcia and Bill Kerr considered themselves responsible pool owners. The Florida couple, who back then had three young children, both worked for a company that sold motorized pool covers. They installed one on their own pool because they thought it was the safest type.

But while they were at work one spring afternoon, the cover was off because the pool had just been cleaned. The nanny was making lunch and did not notice when Cody, 2, slipped out an unlocked door in his parents' bedroom and ended up in the pool. Later, a neighbor who heard the nanny's screams climbed over the fence and pulled out Cody's body, but Marcia and Bill never again saw their son alive.

"It was so unbelievable, such a nightmare," said Marcia, looking back 16 years. "We thought we were very safe because we were knowledgeable about drowning."

Summer is here, and across the Washington region residential pool owners are gearing up for a season of outdoor fun. But as the Kerrs and many other families have tragically learned, having a pool in the back yard poses significant risks to young children. According to "Clear Danger," a new study on childhood drowning conducted by the District-based National Safe Kids Campaign, 859 children ages 14 and under died as a result of unintentional drowning in 2001, making it the second-leading cause of injury-related death among children ages 1 to 14. More than half of all drowning deaths among children ages 1 to 4 are pool-related, whereas most drowning deaths among kids 5 to 14 occur in open water sites such as lakes, ponds or oceans.

The study also noted that an estimated 2,700 children ages 1 to 14 were treated in hospital emergency rooms for near-drowning in 2002. Among children who survive near-drowning, 20 percent suffer severe permanent neurological disability. The typical medical cost for a near-drowning victim is $75,000 for the initial treatment and $180,000 per year for long-term care.

To some experts, the data on childhood drowning point to one conclusion: Backyard pools and young children, especially toddlers, don't mix.

"I would not have a pool in my house if my kids were not good swimmers," said Martin Eichelberger, president and chief executive of Safe Kids and director of Emergency Trauma Services at Children's Hospital. Eichelberger's view stems in part from his recognition that it is almost impossible to closely watch a young child 100 percent of the time. In fact, the Safe Kids study found that 88 percent of 496 children whose drowning death data were reviewed were under the general supervision of another person, typically a family member.

Gaia Phillips, a South Carolina school psychologist, needs no studies to tell her that adult supervision is not always enough. Her son Nicholas, 5, nearly drowned while under the care of his great aunt in 2002. The aunt answered the doorbell and stood inside talking, and didn't notice Nicholas heading out her back door. When she found him about 20 minutes later, he was on the bottom of the pool. A neighbor began CPR until the paramedics arrived. Doctors initially thought he would die, but he survived, and after spending nine weeks in two hospitals, he went home and began a long recovery. Today, Nicholas has no recollection of the event, nor any fear of the water, but he has developmental delays.

Hal Stratton, chairman of the Consumer Product Safety Commission, has made drowning prevention one of the agency's top three strategic goals. He said he believes that "every one of the drowning injuries and deaths is preventable."

Yet Stratton and other authorities said that prevention requires more than general supervision.

"An adult needs to see and hear the young child, and should be in arm's reach of him," when he is near or in the pool, said Eichelberger. Kelly Reed, the business manager at Contemporary Watercrafters, a Gaithersburg-based pool service and supply store, agreed, adding that adults should bring out a portable phone and cooler with drinks so there's no need to go inside.

A designated water watcher -- whether hired or assigned by the homeowner -- is necessary to avoid a situation in which, during a pool party, "everybody is watching the children so nobody's watching the children," said Angela Mickalide, program director of the National Safe Kids Campaign.

Also, adults need to take practical precautions, including:

* Keep children away from pool filters and out of the pool during lightning storms.

* Check the pool area regularly for accident hazards such as glass bottles.

* Keep electrical devices away from pools.

* Have a phone and someone who knows CPR nearby in case of emergency.

* Don't allow diving from the side of the pool.

Providing swimming lessons to children over age 4 may help prevent drowning in backyard pools, as can using personal floatation devices that are certified by the Coast Guard, Eichelberger said. (He does not approve of water wings or inner tubes as safety devices.)

Barriers that prevent children from reaching the pool also help prevent drowning. In many incidents involving children, the kids are assumed to be in the house. The problem is that kids who are drowning can't be heard from under the water.

"Drowning is a silent killer," Eichelberger said, adding that it only takes about two to five minutes for a youngster who is submerged to die or suffer severe brain injury.

Marcia Kerr, who became a drowning and injury prevention expert after her son's death and now works as an investigator for the Consumer Product Safety Commission, said her agency recommends the following four barrier choices (listed in order of effectiveness in drowning prevention). When used together, they create "an obstacle course that the child has to get through" to reach the pool, she said. The barriers are:

* Four-sided isolation fence. Required by law in a few states, including Florida, this interior fence goes directly around the perimeter of the pool. Ideally, it should have a self-latching, self-closing gate and separate the house from the pool. It serves a different purpose than a fence around a yard. "An exterior fence protects the neighbors' children, which is important for their safety and your liability, but provides no protection for your child," said John Hope, a Virginia-based independent dealer for Baby Barrier pool fences.

* Power cover. You can open this type of electronic pool cover automatically by pushing a button or turning a key. It needs to be open when the pool is cleaned, but can be closed easily at all other times when the pool is not in use.

* Door alarm. This device is put on any door that leads to the back yard. It should be placed high enough that an adult can disengage it but a small child cannot.

* Self-latching, self-closing door device. This prevents a child from opening a door and getting out on his own while an adult is distracted.

A pool alarm that is activated when it senses motion in the water can provide more protection. But Kerr advises using such an alarm only in conjunction with other barriers because it won't go off until the child is already in the pool, "so the seconds are ticking away."

Looking back, Kerr wonders whether having layers of protection around the pool might have saved her son Cody. Instead of having just one barrier, a pool cover, that happened to be off at the time, "if he had to go through a door latch, a door alarm and a pool cover, that would have taken a long time," she said.