Never trust a wolf in sheep's clothing. Or as a group of good Samaritans discovered: a wolf in dog's clothing.

Key points: The men rescued the animal from the Parnu river and took it to a clinic for treatment

The men rescued the animal from the Parnu river and took it to a clinic for treatment The "dog", which was revealed to be a wolf, was treated for hypothermia and low blood pressure

The "dog", which was revealed to be a wolf, was treated for hypothermia and low blood pressure It was released back into the wild with a radio tracker after making a full recovery

It's a lesson three construction workers from Estonia learned the hard way after rescuing what they believed to be a helpless dog trapped in the icy waters of the Parnu river.

After clearing a path through the ice, allowing the animal to swim back to shore, the three men dried it with a blanket, bundled it into their car and took it to a clinic for medical care.

It was there that they realised their mistake — it wasn't a dog at all, but rather, a young male wolf.

Though wolves have been known to attack humans, sometimes fatally, the animal was reportedly more interested in a snooze than a snack after its ordeal.

It was only when the three men took the animal to a clinic that they discovered it was a wolf. ( Supplied: Estonian Union for the Protection of Animals )

"He was calm, slept on my legs," one of the rescuers, Rando Kartsepp, told Estonian newspaper Postimees.

"When I wanted to stretch them, he raised his head for a moment.

"The experience was new. We hope he will be fine."

The wolf was reportedly more interested in a snooze than a snack after its ordeal. ( Supplied: Estonian Union for the Protection of Animals )

The wolf was ultimately treated for low blood pressure and hypothermia, before being placed in a cage and released back into the wild with a radio tracker.

The Estonian Union for the Protection of Animals (EUPA), which paid for the animal's treatment, thanked the rescuers for their bravery, alongside the "doctors of the clinic who were not afraid to treat and nurture the wild animal".