Rescuers have released a young humpback whale that became a national sensation after it was beached in shallow waters off the coast in Germany, although marine experts have said its chances of survival are low.

The whale, variously nicknamed Timmy or Hope, was released into the North Sea off Denmark after being transported there in a water-filled barge by rescuers.

The 10-metre long calf swam out of the barge and was later observed blowing through its blowhole and swimming freely “in the right direction”, according to Karin Walter-Mommert from the rescue initiative.

The rescue attempt had been criticised by the International Whaling Commission (IWC) as “inadvisable” because the whale appeared to be “severely compromised” and was unlikely to survive after its release.

Experts from the Oceanographic Museum in Stralsund on Germany’s Baltic coast also recommended the creature should be left to die in peace.

The whale has been described as lethargic and covered in blister-like blemishes, and parts of its mouth are believed to be caught in a fishing net.

The museum’s director, Burkard Baschek, has said trying to save the whale amounted to “pure animal cruelty”.

The rescue attempt was funded by two multimillionaires who said they were prepared to pay “whatever it costs” to release the whale, which became stranded on a sandbank in Wismar Bay near the city of Lübeck nearly six weeks ago.

As its health deteriorated, German officials gave up trying to rescue the mammal, saying they believed it could not be freed.

But after the whale’s plight garnered national interest, with coverage from TV channels and social media influencers, German authorities were persuaded to approve a privately financed rescue plan.

Initial attempts to save the whale with inflatable cushions and pontoons were unsuccessful, but divers eventually managed to help the creature on to a flooded barge , watched by hundreds of onlookers.

The whale left the barge in the North Sea at about 8.45am local time, said Walter-Mommert.

“It is now swimming on its own and freely, and at least for the time being, in the right direction,” she added.

The calf has been equipped with a tracker to follow its movements and Till Backhaus, the Social Democratic (SPD) environment minister for the state of Mecklenburg-Vorpommern said he was hopeful of a “happy end”.

In Germany, supporters have been baking whale-shaped cakes, composing songs about the animal and tattooing their bodies with its image.

However, the site of Timmy’s release is close to Denmark. The Danish environment ministry has told the German TV broadcaster Deutsche Welle it was not planning to rescue the whale if it became stranded again, describing whale beaching as a “completely natural phenomenon”.