The Canadian portion of the dam is being built across the river.
A cofferdam shaped like a horse shoe has been built to completely seal off the river. With the water pumped out, this creates a dry river bed for workers to place pilings and pour concrete for the dam.
Here you see the cement columns on which the dam is built haven't quite reached the Canadian shore yet.
The American side of the dam has pretty much been completed. The cofferdam used to build it has been removed and that half of the river flow restored.