The Consumer Product Safety Commission said it is “urging consumers to stop participating” in the activity adding that the commission “does not know of any safe way to use this product.”

The inflatable, see-through spheres are common at amusement parks, malls and fairs in the US, Australia and Europe. They are frequently used by children.

A rider climbs inside the plastic bubble, similar to a giant hamster ball, and stands up. The ball is sealed with a zipper and floats in a pool or a lake. As the rider walks inside the ball, the ball rolls along the top of the water.

The commission said that it has informed state amusement ride officials of the risks associated with the product. It is also encouraging state officials not to permit the ride in their state.

One key concern is the lack of an emergency exit. The water balls can be opened only by a person outside of the ball, the commission said.

The commission said it is aware of two incidents in which people were hurt.

In the first, a 5-year-old girl in Kingston, Mass., passed out last year while inside a ball for a brief time. In the other, a young boy suffered a broken arm when the ball he was in fell out of a shallow above-ground pool and landed on the hard ground.

Manufacturers, for their part, say the water walking balls are safe.

“There are now hundreds of thousands of the water balls in use around the world being used safely,” said Charles B. Jones, head of Viale Campania in Monza, Italy, who claims to have invented the water sphere 14 years ago.

The 6.5-foot water walking balls contain about 90 minutes worth of oxygen, he said. A ride typically lasts five to seven minutes.

美国政府周四警告消费者说，水上步行球不安全，可能导致窒息或溺水。水上步行球是近年来日渐流行的一种娱乐活动。

美国消费品安全委员会说，他们正“力劝消费者停止参与”这一活动，并称委员会“不知道有任何使用这一产品的安全方式存在”。

这种充气透明球体在美国、澳大利亚和欧洲的游乐园、大型购物中心和露天游乐场很常见。孩子们经常玩这个。

游玩者爬进这个塑料大泡泡（类似于一个巨大的仓鼠球），然后站起来。这个球用一个拉链封口，漂浮在池子或湖里。游玩者在球里走动时，球就在水面上滚动。

委员会称已将这一产品的风险通知了各州的游乐设施官员。委员会还劝他们在自己的州禁止使用这一游乐设施。

委员会说，水上步行球的一个关键隐患就是没有紧急出口，只能靠人从外面把球打开。

委员会称，他们已经知道有两起因玩水上步行球而受伤的事故。

在第一起事故中，马萨诸塞州金斯敦的一位5岁小女孩去年在水上步行球里待了一小段时间就昏倒了。另一起事故中，水上步行球从地上浅水池中滚出来，掉到坚硬的地面上，球里的小男孩把胳膊摔断了。

不过，制造者自己却说，水上步行球是安全的。

自称在14年前发明了水上步行球的查尔斯?B?琼斯说：“现在全世界有数十万水上步行球在安全的使用当中。” 琼斯是意大利蒙扎的Viale Campania公司的老总。

他说，这些直径为6.5英尺的水上步行球内含可以使用90分钟的氧气。通常水上步行球的一次游玩时间为5到7分钟。