BERLIN (AP) — A humpback whale that got stranded in shallow coastal waters in the Baltic Sea has swum free again, and experts hope that they won't have to make another rescue attempt.

The whale, which is 12-15 meters (39-49 feet) long, swam free late Monday from the spot near the German port of Wismar where it had been stuck since the weekend, regional officials said. It initially headed toward the harbor but then turned toward the open sea.

The whale was sighted again off Wismar on Tuesday morning and wasn't stuck, the Ocean Museum Germany said.

An effort last week to rescue the whale from an underwater sandbank at Timmendorfer Strand, a nearby resort town, eventually succeeded with the help of an excavator. But the apparently exhausted whale was soon in trouble again, albeit in somewhat deeper water, and officials banked on giving it peace and quiet to gather enough strength to swim away.

The drama captivated Germans, with crowds gathering on shore while media have sent detailed updates on its progress and streamed live video from the scene.

But the whale is still far from its natural habitat, and faces a huge effort to find its way to the Atlantic Ocean through the North Sea.

“The whale swimming free yesterday is a first very good sign, but the way to the North Sea is still long and we can only keep our fingers crossed that it makes it there,” Burkard Baschek, the scientific director of the Ocean Museum Germany and the scientific coordinator of the rescue effort, told ZDF television.

He said it wouldn't be practical to try to escort the whale on that journey of several hundred kilometers (miles), pointing to whales' ability to dive. “That means that in principle we can only hope that it will make it under its own steam,” he added.

No tracker has been attached to the whale because its skin is in a poor state after long exposure to the relatively low salt concentration of the Baltic.

The whale was first spotted swimming in the region on March 3.

It is not clear why the whale swam into the Baltic Sea. Some experts say the animal may have lost its way when it swam after a shoal of herring, or during migration.