London ? A desperate rescue effort ended in disappointment Saturday when a whale that swam up the River Thames into the heart of London died before it could be returned to open waters.

The northern bottle-nosed whale, 18 feet long and weighing about 4 tons, captivated the imagination of Londoners and much of the world’s media Friday when it sailed past Big Ben and the Houses of Parliament.

It was clear the creature was disoriented and perhaps ill. Rescuers tried to turn it downstream, but the whale seemed disinterested.

On Saturday morning, a decision was made to hoist the whale onto a barge and take it out to open water – a calculated risk because the weight of the mammal out of water tends to stress its internal organs. Thousands gathered on the riverbank to watch as the whale was winched aboard a barge.

The plan was to release the whale into the open waters of the English Channel, about 40 miles downstream, but this turned into an unsuccessful race against time for the slow-moving barge. About 7 p.m. – still two hours away from open sea – the whale suffered convulsions and died.