No not the old fella that you can always find in your local pub, on the bus, or while you are out and about, who has all day to tell you his life story, while you are trying to rush along.
This can be seen on many rivers.
It is the moment the in coming tide, meets the outflowing river water. The smooth water on the left is flowing slowly left to right, the rougher water on the right is rushing right to left. The pressure of the meeting waters, lifts the surface of the water right across the river. I've seen it a few times now, and it looks quite impressive. You can also see it swallow up low-lying sand/mud banks as well.
This front wall was probably only about six inches high, but I have seen them on the River Dee, a couple of feet high and I believe they can reach over four feet high on the River Severn !
