A young minke whale was rescued from a shallow area of London's River Thames on Sunday.
But after officials brought it to another part of the river for evaluation, it slipped loose.
The whale is now missing again and rescuers fear it is injured.
A 13-foot-long injured whale calf is missing hours after rescuers freed it from a lock in London's Thames river on Sunday.
The young minke whale was freed from the Thames' Richmond Lock after it became stuck on boat rollers.
A spokesperson for the Royal National Lifeboat Institution told The Guardian that the whale was "displaying concerning behaviors," and health officials were concerned it may be "unwell."
But after the whale was brought to another location after the rescue, officials lost sight of it overnight, according to CNN.
British Divers Marine Life Rescue team spokesperson Martin Garside told CNN that the whale was brought to a main part of the Thames using an inflatable pontoon, but it "made its own decision" and swam into the main river alone.
"Where it is now, we don't know," Garside told CNN. "It slipped away in darkness as the tide rose last night."
Rescuers are hoping to find the whale on Monday so they can evaluate its health condition.
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