Rotting dead dolphin in Madrid park leaves police baffled (PHOTO)

The decaying carcass of a dolphin found 320km from the sea in a Madrid park has bewildered Spanish police investigating the discovery of the animal remains.

As with many murder mysteries, the peculiar probe began with a dog walker, who stumbled upon the fishy, or should we say aquatic mammal, corpse on a cycle track in the Spanish capital’s Casa de Campo park on Tuesday.

According to El País, Spanish police have been unable to determine where the creature came from and tests are being carried out on its badly decomposed body at the Animal Protection Center at City Hall.

The strange discovery in the landlocked city has led to amateur sleuths posting theories of how the dumping of the body might have gone down.

Many are suggesting that the dolphin was taken from the Madrid Zoo, with - unverified and unlikely - help from staff.

But investigators do not think the animal belonged to the nearby zoo, following denials by operators of the aquarium.

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Ridiculously, others believe the dolphin, which was wrapped in chicken wire, may have washed up in the park due to rising sea levels.

One Twitter user even implied that Russian President Vladimir Putin might be somehow involved...