A sand bar has probably drifted in from a storm blowing in from the opposite direction of the channel. The same thing happens in Santa Cruz and the waves will break as they go over the sand bar.
I've been through inlets and it's amazing at certain times when the tides coming in and the river flows out. Lots of power but never been a problem if the boat driver nows what they are doing. Sand bars are usually constantly changing due to weather and tides so reading the waves is a real benefit. Fun watching thought.