The rocks can be weathered and eroded by the water as the minerals of the water tends to combines with the minerals of the rocks to form clays and these are rich in iron oxides and salts and they are the starting points of the process of chemical weathering that takes place.
As these first combine in the form weak acid known as the carbonic acid and with the passage of time these acids react, the freezing and thawing of the rocks in the small fragments are also known effects of the water in action.