The Zoological Society of London released autopsy results at a news conference after an assessment on how the northern bottlenose whale died on Saturday, a day after appearing in the Thames in central London.
"Sadly, as is the case with many stranded whales and dolphins, a combination of factors was likely to be the cause of death. Those factors include severe dehydration, some muscle damage, and reduction in kidney function," Paul Jepson, who conducted the examination, said. "The animal, once entering the North Sea, would not have been able to feed, and this is the likely cause of the dehydration."
The whale died Saturday during a rescue operation to transport her to the sea on a salvage barge.
The scientists demolished two popular theories: that military sonar signals or parasites from pollution led the whale to go from the deep North Atlantic and into the shallow North Sea and beach in the Thames, reports CBS News' Vicki Barker.
Jepson, who has led government-funded research on why whales have become stranded on British shores, said disease did not appear to be a factor.
"The animal was remarkably free of parasites. I'm pretty sure that when she entered the North Sea, she was probably a very fit and healthy whale," he told a news conference.
The whale was no older than 11, which is young, and no longer reliant on its mother for food.
Scientists will continue to perform tests to determine if the whale had a bacterial or viral infection.
The female whale swam in the shallow waters of the Thames, passing the Houses of Parliament and Big Ben as she captivated onlookers who crowded along the river's banks to watch her progress.
There are questions about how long the whale was allowed to remain in the river and how long she was on the rescue boat.
"This may be the first Northern bottlenose whale rescue in history, and there's nothing in the textbook to tell us how long they can stay out of water," Jepson said.
"We didn't want to leave her on the boat for too long. We just wanted to get her out as far as we could. But her condition rapidly deteriorated and we made the decision to euthanize her. When I was actually drawing the lethal injection, she died."
Becki Lawson, a wildlife veterinarian with the Zoological Society, added: "Really, we all felt that everything that could be done to save the whale had been done."
The British Divers Marine Life Rescue volunteer group spent at least $9,000 on the rescue and is hoping to raise funds for future efforts through an Internet auction of the watering can used to moisten the whale's skin.
"The Thames whale has demonstrated the tremendous interest and wonder expressed in whales and dolphins by the global public, and hopefully highlights the need and desire to conserve wildlife species in general," Jepson said.
The whale's remains have gone to the Natural History Museum, where they will be available to researchers.