This one is made from plastic sheeting forced by the weight of water against sloping metal supports. These sloping supports are held in place by vertical scaffold poles driven in to the canal bed. It's hard to tell from the photo, but it doesn't look like much water has yet been pumped out from this side of the dam.
Incidentally, I don't like Blogger's new way of displaying photos once you've clicked on them. They seem to be smaller than before, and it doesn't help to have the dim remains of the blog around the outside. Also the scroll bar disappears from the original blog once you've closed the photo view.