Brazilian Elodea - SLELO PRISM

Overview

Brazilian elodea (Egeriadensa), also called Brazilian waterweed, is a submerged, perennial aquatic plant in the waterweed family (Hydrocharitaceae). It is rooted in bottom sediments but can also persist as free-floating mats when fragments break away.

Brazilian elodea threatens native aquatic plant communities, fish habitat, water quality, and recreational uses of lakes and rivers by forming dense, monotypic mats that block light, slow water flow, and crowd out native species.

The species is native to South America, including Brazil, Argentina, and Uruguay. It was first recorded in the United States in 1893 on Long Island, New York, most likely introduced through the aquarium trade, widely sold for its oxygen producing capabilities and showy flowers. It can now be found throughout much of the U.S., as well as 27 other countries. To date, all introductions in the United States appear to be male plants, therefor only reproducing by plant fragments, which can attach to recreational boats, trailers, and equipment and spread to new water bodies.

Impacts

Brazilian elodea forms dense underwater and surface mats that significantly alter aquatic ecosystems. These infestations can reduce biodiversity, displace native plants, degrade fish habitat, and interfere with boating, fishing, swimming, and water access.

Once established, this plant can spread very quickly. When these large stands die back, decomposition can lead to low dissolved oxygen levels, occasionally causing fish kills.

Distribution/Habitat

Brazilian elodea has been confirmed in parts of New York State, mainly in the southern most part, but is not yet documented within the Saint Lawrence–Eastern Lake Ontario (SLELO) PRISM region, making it a Tier 1 species. This makes early detection and rapid response critical for preventing establishment.

Habitat

Brazilian elodea grows in freshwater lakes, ponds, rivers, canals, and slow-moving streams. It tolerates both still and flowing water and can grow at depths of up to 20 feet (6 m). The plant thrives in nutrient rich waters with soft substrates such as sand or mud.

Identification

Identification

Growth form: Submerged aquatic perennial that roots in sediment but also forms dense floating mats from fragments.
Stems: Bright green, cylindrical, and can grow 10–15 feet long, branching heavily near the surface.
Leaves: Thin, bright to dark green, arranged in whorls of 4–6 around the stem; with very fine serrations visible with magnification
Flowers: Showy white flowers with three petals, emerging above the water surface on slender stalks in late spring through summer; only male plants occur in the U.S.
Reproduction: Spreads entirely by fragmentation in North America; even small stem pieces with double nodes can root and form new plants.

Brazillian waterweed.. Photo credit: Robert Videki, bugwood.org.

Brazilian waterweed. Photo credit: Leslie J. Mehrhoff, bugwood.org.

Brazillian waterweed. Photo credit, Leslie J. Mehrhoff, Bugwood.org.

Look-a-Likes

Brazilian elodea can be mistaken with American eloda which is native and hydrilla which is invasive. These three aquatic plants can be distinguished by their leaves and roots:

American elodea has smooth leaves in whorls of two to three.
Brazilian elodea has larger, smooth leaves in dense whorls of four to six.
Hydrilla has serrated leaves in whorls of four to eight with rough spines on the underside. Additionally, hydrilla produces small, potato-like tubers in the sediment, which both elodea varieties lack.

A comparison between native American waterweed, invasive Hydrilla, and Brazilian elodea. Source: ausablieriver.org.

Management

Prevention

Clean, Drain, Dry boats, trailers, and gear before moving between waterbodies.

Never dump aquarium plants or water into lakes, streams, or storm drains.

Manual / Mechanical Control

Hand-pulling may be effective for small, early infestations but all fragments must be removed

Mechanical harvesting is not recommended as it creates further fragmentation

Chemical Control

Aquatic herbicides such as fluridone, penoxsulam, diquat, or endothall may be used when and where they are permitted. Herbicide use requires NYS DEC permitting and careful planning to minimize nontarget impacts

Biocontrol

Currently, no specialized biological control agents are widely approved for Brazilian elodea in NY.

Report

Take a clear, close-up photo, note the location (GPS coordinates are best), and report observations to NYiMapInvasives or directly to the SLELO PRISM’s Aquatic Restoration and Resiliency Coordinator, Adrien Owens, Adrien.Owens@tnc.org.

Education and stewardship are the most effective ways to prevent invasive species from establishing. Join our Water Protector’s Program to support early detection of this and other aquatic invasive species. Participants learn to identify and report priority species to NYiMapInvasives and adopt a waterbody for annual monitoring

SLELO PRISM also offers the Aquatic Invasive Species Learning Experience (AISLE), a three‑part training held annually that includes a virtual ID session, a hands‑on workshop, and a guided paddle.