The Mohave County Sheriff's Office said she was located downstream of Topock, Arizona, near the California border.
The crash was so violent that one of the boats sank and the other sustained major damage, fire officials said.
As search-and-rescue crews continued to look for three other boaters who vanished in a popular section of the river near the California-Arizona border, authorities identified the body recovered Monday as Christi Lewis, 51, of California.
Searching for the missing men are rescue boats, divers and helicopters from the Mohave County Sheriff's Office and the San Bernardino Sheriff's Office of California. Nine people were injured, with two in critical condition, authorities said.
Six people had minor injuries and six others suffered injuries that were not life-threatening.
No one on the boats was wearing a life vest, Schuster said.
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The accident happened nearly 300 miles east of Los Angeles along part of the river that runs along the border of California and Arizona.
Lewis was missing since about 8 p.m. Saturday, when a northbound Hallet boat carrying 10 people collided with a southbound Sleekcraft, which carried six people, according to officials.
He says two people are missing and "presumed submerged".
The Mohave County and San Bernardino County sheriff's departments are conducting dive and search operations in the area of the crash, which stretches for about two miles officials said. Divers have been sent into the river, which can run as deep as 30 feet (9 meters).
The Sheriff's Office, which found the body at 7:30 a.m., said it "will continue to patrol the Colorado River until all the unaccounted for passengers are located". Rescuers had to call off the search for the missing until Sunday morning because it was too unsafe to put divers in the flowing water after dark. Efforts resumed after daybreak Sunday, and authorities closed off a stretch of the river where the search was taking place.
The search for two people "presumed submerged" was halted overnight, the San Bernardino County Fire District said in a statement.