This plant can be elusive, as it is hard to see when the conditions are not perfect. Perfect conditions are: a cloudless, windless day with the sun shining directly in the place you are looking, with few floating fragments in the water (not after it rains and no algae blooms). Without these conditions, it is difficult to see more than a foot deeper than the surface of the water. Also, the brighter the sun, the brighter green this plant will appear. Below is a photo of fanwort from the UMass biology department.
Fanwort is a native of the southeastern U.S., but is considered to be a non-native invasive plant in the northeast and nortwest of the United States. The fanwort found in Hickory Hills Lake is called cabomba caroliniana. Fanwort is a rooted submersed plant that may have submersed and floating leaves of different shapes. It generally grows in three to ten feet of water and is found in ponds, lakes and quiet streams.
Fanwort stems are long and much-branched. Fanwort has fan-like underwater leaves, which are about two inches across. The submersed leaves are frequently divided, and are arranged oppositely or in whorls along the stem. The floating leaves are small, diamond-shaped, and are infrequent. Fanwort flowers are white to pink to purplish and are about 1/2 inch across. The flowers are on stalks which arise from the tips of the stems (taken from the Center for Aquatic and Invasive Plans, University of Florida, IFAS)
Click here for a short video on identifying fanwort.
-Photo and drawing by Maine Department of Environmental Protection