They closed this gate on the canal north of McLeod Rd. for maintenance. When they do that, the river reverts to it's natural course to the river instead of the intake/entrance of the canal.
If they didn't have the break wall jutting out into the Niagara River diverting water into the head of the Welland River, there wouldn't be enough pressure to keep the portion of the river upstream of the intake from draining itself. You can see the difference in the natural characteristic of the river using it as a source for the canal made in this pic.