Norfolk Wildlife Trust
Protecting ponds against Crassula helmsii
What is Crassula helmsii?
Crassula helmsii is also known as Australian swamp stonecrop or New Zealand pygmyweed. It is an aquatic plant that was introduced to Britain in the early 20th century and by the 1950s had been reported in the wild. By 2014 the species had spread so much it was found in thousands of UK waterbodies and was banned from sale in the UK.
Why is Crassula helmsii a problem in Norfolk?
Norfolk is home to a very high proportion of UK ponds.
Crassula helmsii grows throughout the year, without a dormant period, and can form dense mats on waterbodies such as ponds and ditches that shade and smother other aquatic vegetation that provides creatures such as frogs, newts and dragonflies a place to hide, feed and lay eggs.
The species is very hard to control and can spread quickly from tiny fragments which can drift in the water or be carried on clothing or animals, including humans, dogs, birds or deer.
Philip Precey
What can we do to eradicate Crassula helmsii from your ponds?
We have a track record in successfully eradicating Crassula helmsii from Norfolk sites – including at NWT Thompson Common nature reserve. This work has protected the site’s rare pingo ponds and the plants and animals that rely on these unique landscape features.
We work alongside landowners across Norfolk to tackle crassula in all types of ponds. The aim is to remove crassula from the infested ponds before it can spread to the rest of the ponds on these wildlife-rich sites.
NWS staff are trained in tried and tested Crassula helmsii survey and removal techniques as well as best practice biosecurity methods.
Alongside colleagues at Norfolk Wildlife Trust, we published best practice guidance on crassula survey and removal in spring 2026 and continue to host crassula training for landowners. By bringing together landowners, contractors, community groups, councils and practitioners together, we will help to broaden knowledge of crassula and proven techniques for removing it from our ponds – helping to stop its spread across Norfolk’s rich network of ponds.
If you are concerned about having Crassula helmsii we can survey your ponds and can provide best practice guidance on surveys and removal through Crassula helmsii training workshops.