Still on the Quest

According to my trusty Websters a canal is an artificial waterway and a channel is either a narrow strait between two landmasses (like the English Channel), the natural bed of a watercourse, or the deeper part of a river, harbor, etc. Given her sentence, neither answer strikes me as being absolutely correct. "The water from the river flows through the _____ into the ocean." Well, yes, it does flow down the natural bed of the river, and the deepest part of the river too (as well as shallow part!), but it could be sent through a canal quite easily. I would have chosen either or.