Farming, by nature, is an ex­­tremely unpredictable and often risky way to make a living. Mark­ets can shift overnight. Crop and livestock diseases, such as the devastating avian flu, seemingly strike out of nowhere. Then, of course, there’s the weather.

Now farmers in Iowa and around the country are about to face another unpredictable and risky challenge from Washington bureaucrats. The "Waters of the United...