Source: Wikimedia Commons
Brazilian waterweed
BeginnerEgeria densa
The classic goldfish weed (Japanese name Ōkanadamo), with narrow leaves in whorls of three to six at each node. It tolerates cold and poor water and grows even floating loose. Naturalised in rivers and lakes across Japan and listed as a Priority Control Alien Species.
About
Egeria densa (Hydrocharitaceae), called Anacharis in the trade and Ōkanadamo in Japanese, is an evergreen submerged plant; GBIF treats it as Elodea densa. It is native to south-eastern Brazil, Uruguay and Argentina. Stems exceed 1 m, branch near the top and carry narrow leaves about 1.5–4 cm long in whorls of three to six, with minutely toothed margins. White three-petalled flowers appear at the surface from about May to November. It reached Japan in the Taisho era, reportedly spreading from plants brought in as laboratory material, and is now established in rivers and lakes on Honshu, Shikoku and Kyushu, where it has displaced the native Hydrilla. Only male plants occur in Japan, spreading by stem fragments. The Ministry of the Environment's alien species list (2nd ed., September 2026) designates it a Priority Control Alien Species that must not be introduced to natural waters. In aquaria it is sold as goldfish weed; it tolerates cold, hard water and weak light and grows planted or floating. Its fast growth soaks up nutrients and helps suppress algae in new tanks, but it needs frequent trimming before it shades other plants. It is widely sold in pet shops and home centres in Japan.
Source: Wikipedia (CC BY-SA 4.0)
Size of the Brazilian waterweed
The Brazilian waterweed grows to Stems 40–100 cm or more long, 2–4 cm wide.
Temperature & humidity for the Brazilian waterweed
The ideal temperature for the Brazilian waterweed is 20〜24℃.
Basic Info
Origin
South America (south-eastern Brazil, Uruguay, Argentina)
Lifespan
Perennial; constantly renews itself from fragments
Size
Stems 40–100 cm or more long, 2–4 cm wide
Temperature
20〜24℃
Watering & Fertilizer
Grows without CO2 or fertiliser; absorbs nutrients from the water
Growing Tips
Lighting
Survives weak light, but stronger light gives denser stems. In poor light it turns pale and spindly.
CO2 & Fertilizer
No CO2 needed. It grows without fertiliser and absorbs surplus nutrients, helping to curb algae.
Water Temperature & Quality
Optimum 20–24°C, tolerating 4–30°C. Hardness and pH matter little; it actually prefers cool, hard water.
Substrate & Attachment
Grows planted or simply floating.
Trimming & Propagation
Grows very fast; cut and replant stems. Fragments root easily.
Cautions
Listed as a Priority Control Alien Species. Never dump it in rivers or ponds, prevent overflow from outdoor containers, and dry even small fragments before binning them.
Brazilian waterweed FAQ
QWhat is the growing difficulty level for Brazilian waterweed?
Beginner. A variety suitable for beginners. No special equipment or experience is required—you can grow it without problems by setting up a basic cultivation environment.
QWhat is the ideal temperature for Brazilian waterweed?
The ideal temperature for Brazilian waterweed is 20〜24℃. Avoid sudden temperature changes and maintain a stable environment.
QHow large does Brazilian waterweed get?
The mature size of Brazilian waterweed is Stems 40–100 cm or more long, 2–4 cm wide. This may vary slightly depending on cultivation environment and individual differences.
QHow should I water and fertilize Brazilian waterweed?
Brazilian waterweed: watering & fertilizer — Grows without CO2 or fertiliser; absorbs nutrients from the water. Aim for appropriate frequency and amount.
QWhat is the typical price for Brazilian waterweed?
The price of Brazilian waterweed varies significantly by variety, characteristics, size, and lineage. Please check GrowerDirect's price guide for the latest market information.
Last updated: September 23, 2026
References & Sources
Edited & verified by: GrowerDirect Editorial Team
The classifications, regulations, and growing data on this page are created and verified based on the primary information database below.
Taxonomy & Authority
Regulations & Conservation Status
Not listed in CITES (no match in Species+). Designated a Priority Control Alien Species (Ōkanadamo) in the Ministry of the Environment's list of alien species that may damage ecosystems (2nd ed., September 2026). It is not a Specified Invasive Alien Species, so it can be sold and grown, but it must not be introduced to natural waters. Never dump it in rivers, ponds or ditches.
Sources: Species+ (CITES listing check) / Ministry of the Environment: List of Alien Species that may Damage Ecosystems / Ministry of the Environment: alien species list, plants (2nd ed.)
Regulations may change. Always verify the latest information with the relevant authorities.
Related Species
Find listings for this species
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