The main message of the Arnol Valle Levinson's conference is that width and depth are important, unlike what has been said. Valle Levinson refers to semienclosed water bodies. Both water exchange and dissolved and particulate material distribution and transportation will be vertically or laterally segregated depending on the width or depth of the systems. The implication of these results is that transportation of contaminants or plankton will be done preferably on a specific portion of the transversal section of the system. Thus, the samples of the dissolved or suspended material will be done exclusively in one profile (on one point) of a transversal section, which will give us an incomplete representation of what happens in the system.