Parents have been warned about the potential dangers of giving their children a "mermaid tail" as a Christmas present.

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.