In a gripping underwater rescue, Spanish divers have freed a 12-metre long humpback whale entangled in an illegal drift net off the Balearic island of Mallorca.

One of the divers said last Friday’s rescue and a little gesture of appreciation from the giant mammal were also a birthday present for her – the ‘best ever’ in her words.

“It was like out of this world, it was incredible, just incredible,” an official said on Tuesday. It was only the third time a humpback has been seen around the Balearic Islands.

The weakened whale had been spotted by a ship about 4.8km off the eastern coast of Mallorca, prompting the marine rescue. They discovered the whale completely trapped in the red fishnet so it could not even open its mouth.

After initial attempts to cut the net from a boat failed, divers joined the effort and plunged into the sea to remove the mesh with their knives in a daring 45-minute operation.

“We kept cutting and cutting and she kind of gave a little wiggle to get herself out of it,” said the official, adding that the mammal then stayed for a bit to regain her strength in the company of the four divers and even gave what looked like “a little thank you sign” before swimming off.

Nicknamed “walls of death” for the quantity of other sea life they catch in addition to the fish they are set for, drift nets were banned by the UN 30 years ago.