Water chestnut (Trapa natans) is a submerged rooted plant that can densely cover shallow areas. This not only deprives the water from dissolved oxygen and other essential nutrients, but can also get tangled in boats, swimmers, and fishing line. On an economic stand point, aquatic invasive species like water chestnut, if not treated, can lower shoreline property values. Photo by: By Krzysztof Ziarnek, Kenraiz (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons