I saw some novice canoeists on a similar outing on the Fox River in Illinois.  They were canoeing down the river at 4 or 5 knots when they came to a low hanging tree that extended out horizontally from the bank about three feet above the water and it knocked them out of the canoe like a football tackle, capsized their canoe and scattered their gear.  Very painful to watch.  We helped them gather their belongings and dignity.