Articles Surveys

Invasive non-native species (UK) – Curly waterweed

curly waterweed

This week’s article by Elizabeth Kimber, part of our invasive non-native species series, focuses on curly waterweed…

Curly waterweed (Lagarosiphon major) is native to Southern Africa. It was first recorded in the UK in 1944, and is widely sold as a garden pond plant.  The introduction of the plant into the wild in the UK, is likely a result of accidental release.

Identification & Ecology
Identification features of curly waterweed include stems that are 3 metres long, strongly curved leaves and the lower leaves always spiral, with upper leaves either spiral or whorled. The plant survives over-winter in the south of the UK, further north the amount of plant material is reduced throughout the year.

Within it’s native range curly waterweed occurs in streams and ponds. In the UK it occurs in still or very slow flowing water, principally in eutrophic canals, ponds, lakes and gravel pits. Rhizomes of the curly waterweed root in the bottom mud and shoots, which reach up to the surface.

Curly waterweed spreads via fragmentation, and is capable of forming dense infestations in suitable habitat, occupying the water column up to 6 metres deep. The primary impact of the curly waterweed is through shading out of other aquatic plants, which can damage the invertebrate communities associated with these.

Dense growth may deplete oxygen levels in water, disrupt natural erosion-deposition processes, disrupt the movement of animals, out-compete native aquatic plants, block light needed for photosynthesis, disrupt predator – prey relationships, prevent wind mixing – leading to localised oxygen depletion, create mosquito breeding areas and increase water temperature by absorbing sunlight, while die-back can increase nutrient loads to the water (NNSS, 2017).

Curly waterweed is also considered to be a threat to tourism, angling, boating and other recreational pursuits which result in economic impacts. Curly waterweed also has the potential to impact hydro-electric power stations.

Legislation which attempts to control the distribution of curly waterweed includes Schedule 9 of the Wildlife and Countryside Act, 1981 (as amended), which makes it illegal to distribute or allow the release of curly waterweed into the wild.

Control Measures
The best method to control the spread of curly waterweed is to prevent its’ release into the wild. This involves checking machinery, equipment and clothing for plant fragments before leaving a contaminated site.

Physical control is challenging as the waterweed is reproduced by fragmentation, whereby fragments float downstream and colonise new areas. However, hand-pulling may be effective for small infestations.

Chemical control can be used, and is effective, however, chemicals can have an adverse effect on any remaining native species they come into contact with. Chemical control in water must be agreed with the Environment Agency.


  • Non-Native Species Secretariat (NNSS) HERE.
  • RAFTS Invasive Species and Biosecurity Programme HERE.

Header Image: GBNNSS ©RPS

About the Author: Elizabeth Kimber works for an ecological consultancy based in Dorset (Lindsay Carrington Ecological Services Ltd). As part of the role she manages the ecological works for a multi-phase development. She conducts protected species surveys and holds a class 1 bat licence, smooth snake and sand lizard licence. She can be contacted via email: liz (at)