A humpback whale that captivated Germany after a dramatic multi-day rescue effort has become stranded again, raising fresh concerns about the animal's survival.

The massive whale, estimated to be 40 to 50 feet long and weighing about 15 tons, was freed from a sandbank at Timmendorfer Strand, a popular resort town on the Baltic Sea, after rescuers dug an escape channel on Thursday (March 26). But on Saturday (March 28), the whale ran aground again, having failed to find its way back to the Atlantic Ocean.

The whale was first spotted stuck on an underwater sandbank in the Niendorf district of Timmendorfer Strand early on March 21. Rescue crews, wildlife experts, and heavy equipment were quickly deployed to the scene in Lübeck Bay, in northern Germany.

Rescuers tried several methods before the channel dig succeeded. Boats were first used to create waves around the whale, but the effort wasn't enough to shift it off the sand. Firefighter drones guiding the rescue were also unsuccessful. A suction dredger failed because the sand beneath the animal was too compacted to remove. Finally, a larger excavator was brought in from Lower Saxony on Thursday to dig the escape trench.

As reported by Euronews, marine biologist Robert Marc Lehmann confirmed Friday (March 27) that the whale had swum through the newly dug channel overnight. Early that morning, the whale was spotted about 300 yards off the coast, being accompanied by a coast guard ship and several boats as it made its way out of Lübeck Bay. But Lehmann cautioned it was "only a small step in the right direction," warning the whale would only truly be safe once it reached the Atlantic Ocean.

Experts believe the whale is likely a young male. The Washington Post reports the animal appears to be the same whale spotted multiple times in the port of Wismar, in eastern Germany, in recent weeks. Sea Shepherd also removed remnants of fishing gear from a humpback whale off Travemünde, a few miles from the rescue site, suggesting it is the same animal.

The whale's renewed stranding on Saturday means rescue teams face another difficult operation, with the animal's health and stamina already taxed by more than a week of struggles in waters that are not its natural habitat. Authorities have not yet announced a new rescue plan.