The competitive interactions of H. verticillata and V. natans clearly could change the phosphorus concentration in water, but the nutrient levels also could impact the competitive interaction outcomes. For instance, as the water in Lake Veluwemeer in the Netherlands cleared because of decreased nutrient loading, the dominant hydrophyte changed from Potamogeton pectinatus to Chara spp.[4]. In mixed cultures at high fertility, H. verticillata was the stronger competitor relative to V. americana, whereas under nutrient limiting conditions, the growth and competitive advantage of H. verticillata over V. americana were both depressed, and V. americana became the dominant species [5].