The Madrid Rio area south of the city has, any new Madrid resident knows, undergone an impressive transformation in the last decade, developing from little more than a rubbish-clogged ditch to a haven for river wildlife from water voles to kingfishers…and surprisingly large carp.

But a whale?

Madrid’s City Hall have so far remained mysterious about the enormous cetacean, except to tantalisingly promise more information soon in a tweet.

They posted photographs of “marine biologists” examining the carcass.

But of course, it's not a real whale: it's a replica designed with the objective of raising awareness about climate change and the global threat to whales and dolphins.

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The life-size, hyperreal statue of a sperm whale is the work of the Captain Boomer Collective,  an artistic group that has been doing the stunt since 2013, when the first whale appeared on the banks of the Thames in London.

Last year, the replica beast from the deep appeared on the banks of the Seine in Paris.

“It’s an artistic way of making people aware of the environment,” Bert Van Peel, the founder of Captain Boomer told Le Figaro at the time.

“These hyperrealist sculptures are an immense metaphor for the dysfunction of our ecological system.”

VIDEO: Drone captures incredible footage of whales off Barcelona