A dead humpback whale is baffling researchers after it was found in Brazil’s Amazon jungle, near the mouth of the Amazon River.

The whale was found approximately 15 metres from the shore of Araruna Beach along the Marajó Bay in Soure, Brazil. Local authorities say spotting a whale in the region at this time of year is quite rare.

According to the Brazilian non-profit environmental group Bicho D’água, the 10-ton whale was eight metres long. But local officials said it was slightly larger, estimating it was 11 metres long.

A team from the region’s Municipal Secretariat of Health, Sanitation, and Environment said the carcass didn’t appear to have any visible injuries.

The two prevailing theories as to how the whale ended up in the brush are either:

  • A powerful tide launched the whale inland, or
  • The whale died at sea and was carried onto the land by people

In an Instagram post, the conservation group explained the creature had not fully matured, saying “it is not an adult animal, nor as large as it seems in the pictures.”

According to National Geographic’s animal reference guide, when humpback whales are fully mature they can weigh about 40 tonnes and grow up to be the size of a bus -- or around 19 metres long.

Until officials conduct a necropsy, it’s unclear as to why or how the whale died. But a member of the conservation group wagered a guess.

Bicho D’água’s project leader Renata Emin told The Independent that she believed the calf had become separated from her mother as they were migrating south.

Between August and November, humpback whales are commonly seen further south on Brazil’s Bahia coast, but rarely are they spotted thousands of kilometres north at the mouth of the Amazon River otherwise.