Salvinia is an aquatic fern with most leaves floating on the water surface, forming mat-like growths.

Stems are 30 cm long, 1 mm to 2 mm thick, with multiple branches. Length decreases with increasing plant density.
Leaves of isolated plants are oval to heart-shaped, flat and as small as 10 mm by 5 mm.

The floating leaves are green, non-wettable on the upper surface and have complex waxy hairs about 1 mm long.

The submerged modified leaves, which act like roots, are short brown hairy stalks ending in hairy filaments up to 50 cm long which look like wet hair.

Salvinia species do not have flowers.

Salvinia reproduces vegetatively by division. Dispersal is by invasive growth or physical transfer of parts of the plant. Daughter plants break away from the parent and may be moved with water currents and the wind.

Careless disposal of aquarium contents results in salvinia being deposited in fresh water. Salvinia has also been used as an ornamental in garden ponds.

It can be confused with Azolla spp in its primary growth stage.

Salvinia is a serious aquatic weed that is a declared noxious plant throughout Australia.

It was first recorded at Luddenham, near Sydney, in 1952 and near Brisbane in 1953 and was thought to have been introduced originally as an aquarium plant.

Salvinia is native to Brazil and has now spread worldwide.

It is listed as a Weed of National Significance in Australia.

The main infestations of salvinia are found in coastal streams from Cairns, in North Queensland, to the South coast of NSW. Infestations have also been recorded near Perth, Darwin, Melbourne and Adelaide.

To date, only isolated infestations have been recorded on inland waterways.

In NSW, salvinia is common in the Tweed, Richmond, Clarence, and Macleay catchments, the central coast and metropolitan areas.

Significant incursions have and still are posing problems in the Hawkesbury-Nepean system and in Wooloombi Brook, near Cessnock.

Salvinia is still found in aquarium and rockery ponds as an illegally-propagated aquatic plant.

It is a weed of still and slow-flowing fresh water.

It is very adaptable and will survive in many climates, although low temperatures will reduce its growth rate. It can withstand an occasional frost, but persistent low temperatures and frosts will kill the exposed portions of plants.

Where a thick mat of weed is present and there is enough protection from frosts, regeneration can occur under favourable conditions from unaffected plant portions.

A thick mat, which can protect and insulate the buds, will also help salvinia survive dry spells. Plants have been known to survive for 20 months under these conditions.

Salvinia can grow over a wide range of water-nutrient levels. Spectacular growth rates though are generally recorded in warm water with high nutrient levels. Under these conditions, salvinia can double its mass in as little as two days.

This ability of the plant to grow rapidly makes it difficult to control. The weed can survive in brackish water, although prolonged exposure to levels of 3000-4000 ppm total dissolved salts will eventually kill the plant. Salvinia will not survive in sea water.

Salvinia has the potential to spread to much of Australia and is regarded as a serious threat to waterways and irrigation areas because it disrupts aquatic ecosystems, seriously affecting native animals and plant life; decreases the quality of water by causing odours, accumulation of organic matter and stagnation of streams; degrades the aesthetic value of waterways;

reduces or prevents the use of waterways for recreation and transport and interferes with the functioning of river control structures, especially during flooding.