One victim was pulled from a car that was found in the Potomac River near the Columbia Island Marina in the Lady Bird Johnson Park on Sunday.
Witnesses reported the car left the northbound GW Parkway and went into the water, according to a spokeswoman for the U.S. Park Police.
News4's Derrick Ward reported the single occupant in the car was dead.
Traffic was blocked for some time along the northbound George Washington Parkway and the Memorial Bridge as crews investigated the scene near the Humpback Bridge along the GW Parkway.
D.C. Fire tweeted their fireboat was assisting Arlington County Fire Department with the investigation.