Aquatic plants are not my strong suit, so I contacted the University of Florida’s Herbarium expect. He identified the plant as knotweed or dotted knotweed, Persicaria punctate. This is a common wetland plant to most of the United States except for some of the states in the West.
Dotted knotweed is a native of Florida and has a 3 to 4-inch flower stalks containing tiny white flowers. Knotweeds are emersed plants, and there are many species. Emersed means the aquatic plant grows above the surface of the water. Submerged plants grow completely underwater, although a few may have floating leaves.
It is important to know the exact type of environment aquatic plants prefer so they will thrive. Knotweeds grow in marshes and swamps, wet forests and ditches. Depending on the species, they may form a low-growing “meadow” near the lake bottom, grow with lots of open space between plant stems, or form dense stands or surface mats. I have seen them grow in consistently moist soil or muck, especially in those ponds where the water rises and falls.