Pony Power! The Wild Horses of Assateague Island
If you read Marguerite Henry's Misty of Chincoteague as a child, you'll remember that the title character came from a wily band of feral horses living on a sandy strip of island just off the coast of Maryland and Virginia. Though beloved as a bedtime story, this was not a complete work of fiction: the horses exist on Assateague Island, fabled to be the descendants of survivors of a shipwrecked Spanish galleon!
Each July, local volunteers round up the horses and swim with the herd across the channel to Chincoteague, where some of the younger members are put up for auction on Pony Penning Day. This keeps the herd at manageable levels, and the proceeds of the auction benefit the Chincoteague Volunteer Fire Department.