[www.tsusinvasives.org] Ecological threat: In smaller populations this plant can provide habitats for many invertebrates, and food for ducks and fish, but when this plant grows to large populations severe ecological changes occur. This aggressive plant is able to successfully invade new aquatic environments and outcompete native vegetation. It forms dense mats which limits sunlight below the surface, reducing oxygen, and killing fish and invertebrates below. As with other invasive aquatic plants, Egeria densa is able to impede water flow which increases flooding risks, and hinder recreational activities. These plant is spread by flooding, waterfowl, and human recreational activities. (link added by Mary Ann Machi)

[Wikipedia] South America native, invasiveness: Egeria densa, the large-flowered waterweed[1] or Brazilian waterweed, is a species of Egeria native to warm temperate South America in southeastern Brazil, Argentina, Chile and Uruguay.[2][3] It is considered a problematic invasive species due to its use in home aquariums and subsequent release into non-native ecosystems. (link added by Mary Ann Machi)