Brazilian Waterweed or Brazilian Elodea (Egeria densa)

Description

Brazilian waterweed is a submersed, freshwater, perennial herb, usually rooted in the substrate but in some cases, drifting. Its stems are cylindrical and simple or branched, and typically grow 1-2 feet long, but can grow up to 20 feet long. Leaves grow in whorls of 3 to 8 with short internodes making the plant look very leafy. The leaves have tiny serrations on the margin and smooth midveins. It has small, white and greenish flowers that extend roughly 1 inch above the water.

Look-alikes

Many other plants look similar to Brazilian elodea and those could be essential to an ecosystem. Brazilian waterweed is often confused with hydrilla (Hydrilla verticillata), American waterweed (Elodea canadensis) and common waterweed (Elodea nuttallii).

Habits & Habitat

Brazilian waterweed is native to South America. It is most prevalent on the west coast and is known in southern Illinois, but is not yet in Wisconsin. It grows in still and flowing waters such as lakes, ponds, pools, ditches, quiet streams and seems to grow best in mildly acidic, nutrient-rich lakes. During winter, it survives along the bottom and resumes growing when waters reach 50 degrees Fahrenheit. It forms mats dense enough to restrict water movement, trap sediment and cause fluctuations in water quality. Reproducing via fragmentation allows it to spread from a single plant and tends to choke out slower-growing native plants. It can also out compete Eurasian water milfoil.

Control

Large infestations of Brazilian waterweed can be controlled with herbicides. Fluridone is most effective but diquat complexed copper mixtures, endothall complexed copper mixtures and endothall dipotassium salt are also effective. In small areas like docks and swimming areas, an opaque fabric can be laid over the substrate to prevent the growth of all rooted aquatic vegetation. Brazilian waterweed can be mechanically removed but this should only be used when all other available approaches are exhausted, as it spreads via fragments.

Additional Information (Links exit DNR)

USDA
USGS
Aquatic Invasive Species
A Problem Aquatic Plant in Washington