It is probably the scariest thing in life. Luckily they got pulled out but were pretty banged up. I was kayaking with some friends and it rained all weekend so the river was nice and the current was amazing. Anyway there is a low head damn, Weir etc( http://en.wikipedia.org/wiki/Weir) that if you do not avoid, you will most certainly die it'll pull you under and you'll drown. But either the current was too fast, or they derped out, but they went over, but luckily the dam workers knew what to do so they got pulled out. I know this might not sound scarey but the low head dam claims many lives each year.
http://www.boatsafe.com/nauticalknowhow/lowhead.htm
https://www.youtube.com/watch?v=P3Rm1KJzVl4