A Vermont man drowned Wednesday as he attempted to swim across a river with his daughter on his back, officials said. The Vermont State Police said troopers responded to a report of a drowning man in the Mad River, at the popular Big Rock Swimming Hole at Kenneth Ward Park in Moretown, at around 5:25 p.m. Wednesday. Witnesses told responding troopers that the man was trying to swim across the river with his daughter on his back when he started to struggle. He went under the water and did not resurface. Bystanders had the water and safely rescued the girl, but could not locate the man. Troopers…