The migrants came from the small South American country of Guyana and from Nigeria and Senegal on the other side of the Atlantic, the human rights department for Brazil's state of Maranhao said in a statement.
There were 25 migrants -- all men -- on the boat and two Brazilians, the navy said in a statement.
The Brazilian pair were suspected of being people traffickers, O Imparcial and G1 news sites reported. They had reportedly spent 35 days afloat but there was no immediate indication of what route they had taken.
The boat, a catamaran, was carrying a Haitian flag, the navy said.
On Saturday, local fishermen found the vessel drifting off the Brazilian coastal town of Sao Jose de Ribamar, south of the Amazon river, the navy said.
An attempt by the authorities to locate the migrant boat from the air failed, so the fishermen towed it to port, while also feeding the stranded voyagers, the navy said.
By the time they got in, the fishing captain reported he had "no more food and water to give, because provisions were ending," the navy said.
Once ashore, they were "given medical attention and food," before being taken for processing by the Brazilian federal police, the Maranhao human rights department said.
"The group will be put into temporary housing provided by the state," it said. "The federal police will investigate the possible committing of crimes against the foreigners in relation to their arrival in Brazil and evaluate their legal situation in Brazil."
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