BERLIN — A stranded humpback whale in Germany ’s Baltic Sea looks weaker, and experts fear it won’t be able to find its way back to the Atlantic despite several attempts at its rescue this week.

A 500-meter (yards) restricted area was enforced around the whale so it could get some rest and hopefully free itself, officials said Sunday in a news conference in the eastern German coastal town of Wismar, near where the giant cetacean has been stuck.

“He would be able to do so if he regains his strength, and that is why we decided to leave him alone, allowing him to actually set off and then successfully leave this area,” said Till Backhaus, the environment minister of the state of Mecklenburg-Pomerania, where Wismar is located.

“But we also have to assume that he is weakened. And he is also sick,” said Backhaus, adding that the humpback whale may have injuries because it came into contact with a fishing net.

Previous efforts to rescue the 12-15 meter (39-49 feet) whale off a sandbank at Timmendorfer Strand beach and in the Wismar Bay with t he help of an excavator and boats, creating large waves to help it swim free earlier this week, captivated Germans — with media sending news alerts of updates on its progress and streaming live video from the scene.

The whale also became a popular topic of conversation across the country, with people exchanging text messages about rescue efforts.

But by now, hopes are dimming that the whale is still strong enough to swim free and find its way back to the Atlantic through German and Danish waters.

“It is very noticeable that the animal is showing significantly less activity,” said Stefanie Groß from the Institute for Terrestrial and Aquatic Wildlife Research at the University of Veterinary Medicine Hannover. “Its respiratory rate has dropped considerably. The animal is not moving. It did not react even when we drove closer.”

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, as it is most likely a male.

The marine mammal cannot survive in the Baltic Sea long-term as the salt concentration of the water isn’t high enough. It has already developed a skin disease. Another issue is that it can’t find the right kind of nutrition it needs, though whales can go without food for weeks.

If it is to survive, it will need to return to the Atlantic Ocean via the North Sea.

“When you consider how narrow the straits are and that there are still about 500 kilometers (310 miles) to go, you realize that it’s a real bottleneck you have to navigate, and naturally, the chances of success are relatively slim,” said Burkard Baschek, the director of the German Maritime Museum in Stralsund.

The whale was first spotted swimming in the Baltic on March 3, but reports of it being stranded surfaced last week.