The problem is that the technical resources required to pull something like this off don't seem to be all that high. You need a ton or so of explosives which is the hard part, a delayed fuse, a water proof container, a camera and light that work underwater, and some winches to deploy the camera and then the bomb. It wouldn't surprise me if almost every nation in Europe could pull this off if they put their minds to it, and a wide variety of sub-national groups as well.