A 46-year-old man from Plymouth drowned Saturday while splashing around the water with his family at William O'Brien State Park, a Washington County Sheriff's Office spokesman said.Chandra Mohan Laghuvaram was swimming in the St. Croix River in water 4 to 6 feet deep when he went under for reasons that aren't clear, Washington County Sgt. James Gribble said.Laghuvaram was at the park with .