U.S. Park Police are searching for a group of men who robbed someone on the bank of the Potomac River in Arlington and forced him to swim across to the District, a spokeswoman said.

The group approached the victim sometime between 6 and 7 p.m. Thursday and took his wallet and cellphone, said U.S. Park Police Sgt. Anna Rose.

Rose said the victim, who was standing by the riverbank near a scenic overlook on the George Washington Memorial Parkway, was then told to swim across.

The victim came ashore near Fletcher’s Boathouse in Northwest Washington and alerted police, who began searching the area for the group.

Rose said authorities detained two suspects, who were later released without charges because they could not be positively identified as the attackers.

A U.S. Park Police officer was also injured during the search. The officer suffered from heat-related distress and was taken by helicopter to an area hospital and later released.

U.S. Park Police ask that anyone with information contact detectives by call (202) 610-8730.