A new study suggests portable or inflatable swimming pools are a greater danger to children than many parents likely realize, leading to one death every five days in the United States during warm months.

Researchers restricted their study to include wading pools less than 45 centimetres deep to inflatable and soft-sided pools measuring about one metre deep.

The study, published Monday in the journal Pediatrics, found that 209 children died in these pools between 2001 and 2009. In addition, there were 35 near-drownings reported during the same time period.

According to the study, 94 per cent of children were under age five and 56 per cent of the victims were boys. The children were also more likely to be in their own yard when the incident happened, with 73 per cent of incidents taking place there.

"The anecdotal evidence was suggesting that because portable pools are readily available in many convenience stores and malls, and they're relatively cheap, parents would pick them up, take them home, quickly assemble them, and all this would be done without a lot of forethought about the safety aspects," said senior author, Dr. Gary A. Smith, director of the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus.

The study is the first U.S. research to probe the role portable pools have played in deaths or near-drownings.

The researchers acknowledge that no single strategy can completely prevent a death or near drowning, and so advocate a multi-pronged approach. On the one hand, manufacturers should develop affordable safety devices for portable pools, including fencing, alarms and safety covers, which are common for in-ground pools.

They also say better consumer-education programs are needed to make parents aware of the pools' risks.

According to the study, children were under adult supervision in only 43 per cent of the cases.

Barbara Byers, public education director of the Lifesaving Society, says the findings are a concern in Canada, where there are fewer pool drownings each year, because there are no safety regulations for portable pools in Canada.

In-ground pools must have fencing on all four sides, while portable pools can be put anywhere on a property, she said.

Also of concern, Byers said, is that many consumers assume such pools are safer because of their smaller size.

"I think many people may think, ‘Oh well it's just a couple of inches of water,'" Byers told CTV News Channel in an interview Monday evening. "But a person, a child, can drown in a couple of inches of water very, very quickly, and very silently."

Byers said access to portable pools should be restricted to the same degree as in-ground pools, and stressed the importance of adult supervision.

"It's really important to have layers of protection to keep young children away from that pool unless you know that you are there with them and you are watching them and keeping them within arm's reach," Byers said. "Most children have no fear whatsoever. It's almost a magnetic attraction to the water. If they see it, they are going to want to go to it."

With files from The Associated Press