After a good walk I found the wreck and photographed it. The long handforged nails looked very sharp and dangerous. I guess it would have been a fairly large barge, but it was impossible discern the actual shape of the hull. Farther inland I photographed a couple of ww2 Sherman tank turrets. These were encased in concrete to form stationary defenses in the Fifties. I'm not sure if the whole tank was encased or just the turrets, but is a strange sight. See all photos here
If you look at the GPS track you can see how I walked the riverbed in some places. Due to the low water level I kept my feet dry.