The Erie County sheriff's office says the woman was wearing a wetsuit and identification papers and multiple plastic packages containing newspaper and letters were duct-taped to her body.
The body was discovered Sunday morning on the west Niagara River shoreline on Grand Island, north of Buffalo.
Authorities say the woman may have drowned while trying to illegally enter the United States from Canada by swimming across the river.
Investigators say they are withholding the name of the woman for now.
An autopsy has ruled the death a drowning.