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Giant salvinia

Why is it a threat?

Giant salvinia (Salvinia molesta) can completely cover waterways preventing the passage of sunlight and oxygen that native plants, fish, insects and other species require. It makes lakes and streams look like putting greens, eliminating opportunities for boating and fishing.

How did it get here?

Native to southeastern Brazil, this water fern was probably initially spread to different parts of the world by the aquarium and garden-pond trade.

How does it spread?

It can be spread accidentally from site to site by boaters. Since giant salvinia can double its numbers in as little as 2-10 days and cover the entire surface of a body of water, even extremely small fragments of the plant can rapidly alter our lakes and waterways, potentially making them unusable for future recreation.

How can you remove it?

Giant salvinia produces so rapidly that large infestations in reservoirs and rivers are virtually impossible to eradicate by hand. However, small infestations in ponds and streams can and should be controlled by hand immediately, before they get too big. A biological control agent is being tested but is not yet approved for use in the U.S. A weevil that naturally keeps salvinia in check has been used in more than 13 countries. If you find giant salvinia growing outdoors anywhere, please contact the Invasive Species Initiative at invasivespecies@tnc.org. If you have it in your aquarium or garden pond, remove it and let it dry completely. If possible, compost the dried plants, which will kill them entirely and minimize the chances that a small fragment is inadvertently dumped near a river or storm drain.

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