Lifeguards simulate a shallow water rescue in a wave pool in Ypsilanti, Mich. Concern is growing about risks present even when the depth at most park attractions is less than 3 feet.

YPSILANTI TOWNSHIP, Mich. — With their appealing slides and wave pools, splashing around at waterparks is an increasingly popular way to spend a summer day. But the shallow waters belie hazards that experts say visitors who are focused on the fun may be underestimating.

As the parks proliferate, concern is growing about the risks present even when most of the water is shallower than 3 feet — people who aren't good swimmers mixed with the unexpected hit of waves and falls that can lead to concussions or even drownings. The American Red Cross, a leading trainer of lifeguards, has taken note and added training for extreme shallow water rescues.

“We pretty much have an ambulance call every weekend,” said Brian Machemer, superintendent of the Rolling Hills Water Park in Ypsilanti Township. He added, “On average, we probably have a pull-out a day. Now, that isn't always a serious incident. But it's somebody who's struggling that we feel we need to help out.”

While no figures are available for overall waterpark injuries, the Red Cross cited U.S. Consumer Product Safety Commission estimates when it launched its updated training efforts this year. Those show about 4,200 people a year taken to emergency rooms to be treated for scrapes, concussions, broken limbs, spinal injuries and other such injuries suffered on public waterslides. Those numbers, though, do not include other waterpark injuries or those who need lifeguard assistance without a hospital trip.

“You're in an environment that is extremely fun but can be extremely dangerous if you're not vigilant,” said Roy Fielding, a specialist in lifeguarding and water safety who is on the Red Cross Scientific Advisory Council.

In July alone, one drowning and at least three near-drownings were reported at U.S. waterparks. A 5-year-old girl drowned in a shallow area of a wave pool at a municipal-owned waterpark in Grand Island, Neb. The wave pool was not operating at the time.

About 1,300 waterparks are operating in North America, up about 30 percent from a decade ago, according to the trade group World Waterpark Association.

Those parks attracted about 83 million people in 2013, compared to about 73 million in 2004.