Fresh water is very very important in our life. Much of what was said about estuaries also applied to freshwater marshes, they tend to be naturally fertile ecosystems. Tidal action, of course, is absent, but periodic fluctuation in water levels resulting from seasonal and annual rainfall variations often accomplishes the same thing in terms of maintaining longe range stability and fertility fires during dry periods consume accumulated organic matter thereby deepening the water holding basins and aiding subsequent aerobic decomposition and release of soluble nutrients, thus increasing the rate of production. In fact, if such events as drawdown and fire do not occur, the build up of sediments and peat (undecayed organic matter), tends to lead to the invasion of terrestrial woody vegetation. Where man controls water levels by dikes in marshes he generally finds that chemical herbicides or mechanical methods have to be used if the area is to continue to exist as a true freshwater marsh ecosystem suif able for ducks and other semiaquatic organisms.

    The general public prejudice against marshes is understandable, since they are sometimes the home of mosquitoes and other disease carriers and pests. Before much was known about the life history and ecology of the arthropods and anails as disease carriers, destroying their habitat (that is, draining the marsh) was about the only solution. Our present knoledge now makes it unnecessary to destroy the ecosystem in order to control undesirable species.

     In addition to producing ducks and fur bearers, marshes are valuable in maintaining water tables in adjacent ecosystems. The florida everglades are an exceptionally large and interesting stretch of freshwater marshes characterized by naturally fluctuating water levels. Complete drainage (even if possible or otherwise desirable) would not only ruin the area as a wildlife paradise but would also be  risky in that salt water might then intrude into the underground water supply needed by the large coastal cities. Likewise, complete stabilization of water levels would also destroy the unique features of the everglades, for reasons given at the beginning of this section.

     Finally, it is significant that rice culture, one of the most productive and dependable of agricultural systems yet devised by man, is actually a type of freshwater marsh ecosystem. The flooding, dranining, and careful rebuilding of the rice paddy each year has much to do with the maintenance of continuous of continuous fertility and high production of the rice plant, which, itself, is a kind of cultivated marsh grass.