The pool toys attempt to allow users to swim like a mermaid, either binding their feet into a single fin, or both legs into a tail. 

NSW Fair Trading Commissioner Rod Stowe and consumer advocacy group CHOICE issued a warning about the toys on Saturday, urging parents to think twice before buying them. 

A Fair Trading spokeswoman said there had been no reports of the tails causing injury or drownings in Australia and the caution was a pre-emptive one ahead of Christmas.

The warning points to a video from the US published online in June, which shows a young girl wearing a mermaid tail appear to become stuck upside down under the water. The girl's mother quickly goes to aid, before saying "I don't think that's a good idea".

Mermaid tails are not banned in Australia.

Commissioner Stowe said they usually come with an age recommendation of six-plus years, advice that the child needs to be a good swimmer, must be supervised and may require a lesson in how to use the tail and are not to be used in shallow water.

"These aquatic toys could present a risk for a young child, particularly if they are not a strong swimmer. The video is quite harrowing and should serve as a timely reminder to all parents to be vigilant about water safety," CHOICE spokesman Tom Godfrey said.

Australia's largest toy retailers, such as Toys R Us, Big W and Target, do not sell "mermaid tails", according to their online catalogue. 

But the fins and tails, which range in price from about $20 to $700, are easily available to purchase online, with several local supplies listed.

A spokeswoman for one said the products that bound the whole leg were more dangerous than the mono-fins because they required practice to be able to use and a higher swimming skill.  She said the products should never be used by children without parental supervision and were intended to cultivate a love of the beach and water.

It appears the sale of mermaid fins and tails has taken off on the back of a cultural movement known as "mermaiding",  essentially the act of binding your legs and feet together in order to look like a mermaid. There is now a collection of professional mermaids who are hired for appearances in films, music videos and advertising campaigns. In addition, swimming with a mermaid tail has become a form of fitness workout. 

West Australian Consumer Protection acting commissioner David Hillyard also issued a warning about the tails to parents last week.

But mermaid tails are not the only toy that have caught the eye of authorities this Christmas.

Roads Minister Duncan Gay has warned parents not to buy their children hoverboards, also known as self-balancing scooters. The devices, which are usually priced between $200 and $500 and can reach speeds up to 26km/h, are illegal and anyone caught riding them risks a hefty fine, the minister said.

"They don't have adequate brakes and don't have lights or warning indicators, meaning they can't interact safely with other road users like pedestrians," Mr Gay said. "What's more, riders endanger themselves because they're unprotected around other vehicles like cars and trucks."