These are a special kind of frequently fatal trap for a paddler. The picture is of a fish ladder, the steps are only about 18”, and the water is flowing faster than you could walk, but a fast sprinter might keep pace. If you canoe was three feet long these would be a nice scale model of a low head dam. The second picture shows the problem. The water from the top edge of the photo is traveling towards the bottom edge; the water at the bottom is going back up stream at the same speed it is traveling over the drop at. The water at the surface is traveling up stream—not flowing down the river. The water rolls over itself many times before getting to the bottom of the face of the drop and finally flushes downstream. In this case the out flow is almost 10 feet downstream—and this is a tiny drop. A dam as low as three foot tall with a moderate flow over it is more than sufficient to roll a canoe and it’s passengers over and over till the hull is so much flotsam and the passengers are drown. How do you deal with these? Avoid them is best; get out and carry around them. Be aware that anytime you see a straight line on a river it is a danger sign. It is a sign of a terrain change—might be a dam, a waterfall, or the start of rapids; always scout straight lines on unknown rivers. If you having to end up going over a low head dam do it with gusto, paddle hard and stay straight and don’t stop paddling until you are well down stream of it. If you screw up and end up parallel in the trough, lean downstream on a high brace, reach as far down stream as you can and put in an almighty powerful draw stroke to try to pull the bow up over the wave. The other thing to do is work your way to the edges of the dam where the water does flow out of the trough. And be thankful you’re in a canoe on your knees as it’s a good position for talking to your God. If you capsize and are getting turned over and over (window shading is the term white water folks call this – indistinguishable from a death roll as far as I’m concerned) Try reaching to the bottom where the water is flowing out, you might be flushed out. It also one of the few times shedding your PFD and being less buoyant might save you.