A 36-foot-whale caught on a man-made sand bank in The Wash in Lincolnshire since Sunday morning has died.
Volunteers worked for more than a day to try to free the whale, but failed to budge the 15-ton animal.
The whale died just before noon on Monday, a rescue spokesman said.
Inspector John Bow of the RSPCA said: "It was a deepwater animal and shouldn't be there, it has obviously lost its way."
The team had resumed efforts to free the 15-ton animal from a sand bank at Sutton Bridge in The Wash shortly before the 0700 GMT high tide.
"We were not really equipped to lift an animal of this size so this is really a last-ditch attempt," said Alan Knight from the rescue team.
The whale was spotted by a member of the public at about 10am on Sunday.
It is not known how it came to be on the bank.
It might have become stranded due to ill health, or it could have been confused by the sand banks and shallow water of the The Wash.
Volunteers spent Sunday trying to keep the whale upright so its lungs did not collapse under its own weight.