Authorities say a group of men robbed a person on the bank of the Potomac River in Arlington before forcing him to swim across it.

U.S. Park Police spokeswoman Sgt. Anna Rose tells the Washington Post (http://wapo.st/2bscn79 ) that the victim was standing by the riverbank on Thursday when the group approached him and took his wallet and cellphone.

Police say the man was then forced to swim across the river to the District of Columbia. Rose said he made it to the other side, where he alerted authorities.

Rose said two suspects were detained but were later released because they could not be positively identified as the attackers. U.S. Park police are asking anyone with information about the incident to contact authorities.