The woman was visiting the falls with a friend at about 8:30 p.m. Sunday when she climbed over the railing and straddled it while holding an umbrella.
The woman apparently lost her balance and fell into the water when she stood up to climb back over, police said. She fell into the swift-moving river about 80 feet upstream from the brink of the Horseshoe Falls.
"It appears from the review of surveillance video that this incident was a tragic accident," a Niagara Parks Police news release said.
The department said it was working with the Japanese consulate general to notify the victim's family. Her name was withheld pending the notification.
While the woman's body had not been found, crews found the remains of an unidentified male from the whirlpool below the falls. Police said his death appears to be unrelated.
The Associated Press contributed to this report.