QUINCY, Ill. - The FBI is trying to solve a mystery surrounding the report of a possible hostage situation involving two Minnesota residents.

Authorities believe a woman in her 50s left the Twin Cities with a man on Sept. 5.

The Adams County Sheriff says that a 911 call at about 11 a.m. on Friday said that there was a possible hostage situation going on in Quincy, Illinois.

Authorities swarmed an area along the Mississippi River. They found the woman too weak and tired to get out of this small boat.

Witnesses watched as investigators arrested the man she was traveling with.

"Obviously, you're kind of on edge," a witness said. "You're very alert to what's going on."

The woman is being treated at a hospital in Quincy.

Authorities are not saying whether the woman went with the man willingly.

The FBI investigation is ongoing. The Coast Guard is assisting in the investigation.