Potamogeton crispus

A naturalized invasive plant of shallow water. It is the only species of pondweeds in North America with serrate leaves, so can be identified easily. The leaves are entirely underwater and the flower extends above the water surface. Most of the plant disappears by midsummer; new plants (small) emerge in late summer and overwinter. Because rapid growth begins in very early spring, this species can outcompete native aquatic species for light and space. It can also slow water flow and cause stagnant conditions.