Attempts to rescue a young humpback whale that was stranded in shallow waters off the Baltic coast in Germany have been criticised by the International Whaling Commission as “inadvisable”.

The 10m-long whale, variously nicknamed Timmy or Hope, swam on to a sand bank more than a month ago, and its health deteriorated as it repeatedly became stranded. Hopes were raised on Tuesday when divers helped the mammal on to a flooded barge. By Wednesday, the barge, pulled by a tug boat, had reached Danish waters as it headed towards the North Sea.

But the IWC’s Strandings Expert Panel said that the creature “appeared to be severely compromised” and “unlikely to survive” even if attempts to move it into deeper water were successful.

Till Backhaus, the environment minister for the state of Mecklenburg-Vorpommern said that if the whale was in good health, it would be released in the sea.“Something like this has never happened before in Germany, where a life-saving operation of this kind has been carried out,” Backhaus told reporters. “And this was an experiment, and the experiment was a success, and that’s wonderful.”

The minister said the whale was resting peacefully, adding that on Tuesday night it had vocalised.

The current mission is being financed by two multimillionaires, who have said they hope to save the mammal “whatever it costs”. It has sparked a national whale frenzy, with supporters doing everything from baking whale-shaped cakes, and composing songs about the animal to having themselves tattooed with images of the animal.

But local experts from the Oceanographic Museum in Stralsund have also warned that attempts to save the whale were in vain and said the whale should be left to die in peace.

The creature has been described as lethargic and covered in blister-like blemishes. Parts of a fishing net, some of which was removed early on in its stranding, is believed to be still caught in its mouth. The museum’s director, Burkard Baschek, said: “A rescue attempt … is no longer worthwhile … this has been confirmed to us repeatedly by international colleagues.”

He said continuing to try to save it amounted to “pure animal cruelty”.

On Wednesday, the same group of experts warned against letting it loose in the open sea, saying that it was in danger of drowning. It urged the team behind the operation to be transparent, including providing data on the creature’s whereabouts and release location if it is freed.

The IWC said that active interventions to save stranded whales “including refloat or translocation attempts such as towing or moving by barge” were “inadvisable on grounds of both animal welfare and human safety”.

“In our assessment, these interventions, although well meant, impose very considerable additional stress upon a creature that is already gravely ill, to little ultimate benefit.”

The animal has been attached with a tracking device and is being accompanied by a support team which includes vetinarians.

In the event of the animal’s death, the IWC said, work to recover its remains, carry out a detailed necropsy and safely dispose of its remains should be carried out as soon as possible.