Densities of several hundreds of micrograms of algal chlorophyll a per square meter are not unusual on submerged plant surfaces. Frequently, the supporting surface cannot be seen through the covering mass, which may compete with the plant for light, inorganic carbon, and nutrients. Given the problems posed by the overlying water column as well as the periphyton (syn: epiphyton) for such plants, it is remarkable that submerged plants develop at all in other than the clearest, most nutrient-deficient waters.