Aquatic Weeds in the Ross River

A wide view of the Ross River with its surface heavily covered by a thick mat of green aquatic weeds, with trees lining the banks.

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Featured Image: TheDinosaurMan08, CC BY-SA 4.0 Wikimedia Commons

Sagittaria/Delta Arrowhead (Sagittaria platyphylla)

Delta Arrowhead, Arrowhead, Slender Arrowhead. A close-up of the invasive aquatic weed Sagittaria, showing its large green leaves and clusters of small white flowers.
Show_ryu, CC BY-SA 3.0 , via Wikimedia Commons

Sagittaria first appeared in the Ross River in 2012. A containment program now targets this highly invasive aquatic weed to eradicate it before it spreads across the region. It chokes shallow waterways—including irrigation channels—blocking water flow, fish movement, and recreation. Farmers in the Murray-Darling Basin spend over $2 million annually to control Sagittaria and restore irrigation channels, highlighting its immense economic toll.

Water Hyacinth (Eichhornia crassipes)

Water Hyacinth, Water Orchid, Nile Lily. A close-up of the invasive water hyacinth (Eichhornia crassipes) with its light purple flowers and glossy green leaves floating on the water's surface.
Juan Carlos Fonseca Mata, CC BY-SA 4.0 , via Wikimedia Commons

Water hyacinth, a floating weed, forms dense mats atop water bodies. It boasts light purple flowers and round, dark green leaves. Originally introduced from Brazil as an ornamental pond plant, this weed now restricts wildlife migration, depletes oxygen levels, and hampers recreation with its thick cover.

Cabomba/Fanwort (Cabomba caroliniana)

A view of the invasive aquatic weed Cabomba caroliniana growing densely underwater, with some small fish and lily pads on the surface.
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, CC BY 3.0 , via Wikimedia Commons

Cabomba grows fully underwater—except for its flowers—in slow-moving or still water, creating a thick canopy below the surface. Its stems stretch up to 10 meters long, posing risks to swimmers who may tangle in them.

Water Lettuce (Pistia stratiotes)

An overhead view of a body of water completely covered by a dense mat of the invasive floating weed water lettuce (Pistia stratiotes) and duckweed.
W. Bulach, CC BY-SA 4.0 , via Wikimedia Commons

Water lettuce, a floating weed, features spongy, fan-shaped leaves. It forms dense mats that shade out other plants. It reproduces via seeds or runners that spawn daughter plants. With a rapid growth rate, water lettuce spreads quickly under favorable conditions, covering entire water bodies. Water movement, natural or via boats and gear, typically spreads its seeds.

Hymenachne (Hymenachne amplexicaulis)

A dense stand of the invasive grass Hymenachne amplexicaulis growing in a shallow, wet area with green leaves and tall stalks.
Photo © Chris Gardiner, James Cook University — US Forest Service, Pacific Island Ecosystems at Risk (PIER), Public domain, via Wikimedia Commons

Hymenachne, a grass with long, wide leaf blades, thrives in shallow water or along riverbanks, reaching up to 2.5 meters high. It forms dense stands that boost flood risk by slowing drainage channels. These stands also limit animal migration and shrink available habitat.

Salvinia (Salvinia molesta)

An overhead view of a body of water completely covered by a thick mat of the invasive floating fern salvinia (Salvinia molesta).
Vengolis, CC BY-SA 4.0 , via Wikimedia Commons

Salvinia, a free-floating, spongy weed, flourishes in slow-moving, nutrient-rich, warm water bodies. It removes habitat, shades the water column, and cuts oxygen levels, degrading water quality. Its small, folded leaves sport tiny hairs, and its roots dangle freely. Without flowers, salvinia spreads solely through live material carried between water bodies.

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