What Does the Specialist Say About This:  Watermeal is difficult to control.  The only thing close is fluridone-containing compounds  These aquatic herbicides work if there is no water exchange in the pond, but only limited control can be expected and they are expensive.  Nutrient reduction, if feasible, may lessen the problem over time.  On the bright side, there is a new herbicide, Clipper (active ingredient is flumyoxazin), that should be registered by November 2010.  It is reported to be effective, and it worked outstandingly in one trial I conducted.  The price of this new aquatic herbicide has not been set.  Kenneth A. Langeland, Ph.D. Professor-Aquatic and Invasive Plant, UF Department of Agronomy