I have a pasture pond that is just under 1/2 acre in South Central Michigan. According to the National Weather Service, we have had abnormally low precipitation this summer . My pond sits out in the open field unprotected from the wind. This summer I lost 27 inches on my pond, so I learned about evaporation. In fact, According to a University of Montana Experiment station: shallow ponds(those under 17 feet deep) in the Midwest can loose up to 1 1/2 inches a day; and some parts of Arizona can loose up to 3 inches a day. I know I get excited when my pond goes down and there are plenty of people that will say you have a leak when it's simple evaporation. If you have a waterfall or some kind of water feature you can loose more. I also found out that you need at least 18" of water in your pond so your fish don't get froze out. I was suprised when my new pond did not freeze over at all last winter; and I live in Michigan! smile