By Gary Duffy
BBC News, Sao Paulo
A 5.5m long minke whale has been spotted more than 1600km (994 miles) from the Atlantic Ocean, deep inside the Amazon rain forest.
The whale ran aground earlier this week but after being freed with the help of vets and biologists it disappeared shortly afterwards.
It is the second time this week in Brazil that a lost animal has been spotted in an unexpected location.
The minke whale ran aground on a sandbar deep inside the Amazon.
Local people had been splashing water on the whale's back and fin while it was exposed to the hot Amazon sun.
The whale is said to weigh about 12 tons.
Reports of a mysterious animal in the area had been causing alarm among locals near to the Tapajos river, a tributary of the Amazon.
Experts say the animal could have been in the area for a couple of months.
After the whale was freed, helicopters and boats were involved in a search of the area but nothing was found.
A biologist said it was thought the animal became separated from its group and swam upstream, until it ran aground near Santarem in Para state.
While it is not unprecedented, it is unusual for whales to venture so far into fresh water.
The whale is not the only animal to get lost in Brazil this week.
On Thursday a young reptile - which was 1.5m long - turned up at a popular beach in Rio de Janeiro and had to be rescued by firemen.
They had been searching for the alligator for some time and had closed Barra beach, but despite this some swimmers insisted on entering the water.
The caiman, or yellow stomach alligator as it is known in Brazil, was taken to a local zoo for treatment for a broken leg.
This endangered species is normally found in freshwater swamps and marshes, and the fire service in Rio said it was the first time they had rescued one from the sea.