About 100 wild ponies made their way from Maryland's Assateague Island to the town of Chincoteague, in Virginia, in the Chincoteague Pony Swim on Wednesday.
The crossing, which started at 7am and lasted about 18 minutes, is part of a tradition to manage wild pony populations on the island.
Once a year, Chincoteague's "salt water cowboys" will sort out and guide the ponies from the island to the river crossing - just south of the Maryland-Virginia border - that stretches for about 400m.
Some of the ponies are put up for auction the next day, with proceeds going to the Chincoteague Volunteer Fire Department, reported Virginia TV station WAVY.
The event, which is in its 92nd year, draws thousands of tourists and was memorialised in American author Marguerite Henry's children's book Misty Of Chincoteague.
Mrs Chris Smith from Austin, Texas, told The Virginian-Pilot that her daughter Marley, 11, is a big fan of the book and seeing the ponies was her daughter's dream. "It was so beautiful. It was magical. Even I got a little emotional," she added.