Montgomery County Fire/Rescue recovered a young man's body from the Potomac River in the area of Swains Lock near Great Falls Park Friday.
Witnesses on the Virginia side of the river saw the man enter the water south of Riverbend Park in Fairfax County, police say. A witness called 911.
Montgomery County Police detectives believe the man waded into the middle of the river and drowned. He was trapped under a rock.
The man, described as a white male in his late teens or early 20s, has not been identified.
Montgomery and Fairfax County Police are working on the case. They say there is no evidence of foul play.