Lehmann, who had led the attempts to coax the whale into the channel, said the mammal was not yet safe and it was crucial that it remained in open water in Lübeck Bay so that it could then swim out into the wider Baltic Sea.
The whale was escorted by several boats including the coast guard, and there were initial concerns on Friday morning that it was swimming backwards and forwards in a zigzag pattern and might return to the sandbanks.
After several hours, the whale appeared to have swum some distance from the sandbanks, although it was still visible from the shore and had still not completely left the bay.
Lars Hoppe, one of the team who dug the channel enabling the whale to swim away, was convinced it had been desperate to escape.
“He still had a lot of life in him – you could feel it. He wanted to break free,” he told regional broadcaster NDR. “I’m happy he’s managed to do it, and above all I think it’s great that he’s done it by himself.”
Rescuers were unable to fit a tracker to its skin because of its poor condition, and a piece of netting is lodged in its mouth.
Local mayor Sven Partheil-Böhnke also said he was delighted that the humpback had managed to free itself and experts were optimistic that it would continue to swim north in the direction of Denmark.
Even if the whale reaches the Baltic, rescuers believe it needs to swim on into the North Sea and then the Atlantic before it reaches its natural habitat.