The spread of invasive non-native plants along the River Avon and its tributaries threatens the future survival of our native wild plants and animals. In 2012, the Environment Agency, Wiltshire Wildlife Trust, Hampshire and Isle of Wight Wildlife Trust, Natural England and Dorset Wildlife Trust formed the Source to Sea Project to remove problem species from the entire length of the Hampshire Avon. We target plants such as Himalayan balsam, Japanese knotweed and Giant hogweed and work to respond to new pests such as killer shrimp. The project covers the entire River Avon catchment from its headwaters in the Vale of Pewsey, down through Salisbury into Hampshire, to where it flows into the sea at Christchurch.


What are invasive non-native species?

Plants and animals (such as signal crayfish and American mink) that have been introduced to a place where they do not naturally occur are known as non-native species. A few of these are ‘invasive’ and can rapidly multiply and threaten natural habitats. The problem is particularly severe along rivers, which can provide pathways for infestations.

A stand of Himalayan Balsam on the banks of the River Nadder.Creeping Water Primrose can take over ponds and lakes completely.

Why are they a problem?

Invasive non-native species upset nature’s balance. They can smother or kill native wildlife, spread disease, cause serious bank erosion, increase flood risk and provide a risk to human health and safety. Once problem plants gain a hold on our river banks and wetlands they will take over, spreading at astonishing speed. When native plants disappear the whole food chain of the river system starts to break down. Without effective control now, this could lead to a permanent loss of native wildlife and plant species.


What has the project achieved so far?

During the past four years, we have been able to deal a significant blow to invasive species in the catchment. Supported by our army of volunteers we have surveyed and targeted hundreds of kilometres river bank for Himalayan and Orange balsam, successfully treated dozens of sites with Giant hogweed and Japanese knotweed, have very nearly eliminated Creeping water primrose from Braemore marsh and we have worked hard to reach out to a whole range of different communities across the catchment. But there is still work to be done! New nuisance species are knocking on our door and we have to keep working hard to stand our ground.

An extensive summary of the project's achievements in the first three years (2012-2015) is available here for download.


What can you do?

  • Become a river guardian and frequently monitor a stretch of river you own, know or fish for invasive species. We can provide identification training and a group of volunteers when you have an outbreak you can’t control yourself.
  • Volunteer to help us pull Himalayan or Orange balsam during the summer. The 2017 Balsam Bashing programme is available for download here.
  • Let us know if you have spotted an invasive species on the riverbank so we can build an up to date distribution map of invasive species in the Hampshire Avon catchment (and outside).
  • But above all; make sure you don’t (incidentally) introduce any non-native species into the environment – the consequences could be devastating. Always Check, Clean, Dry!

If you are interested in helping out with any of the opportunities above, please contact us for more information, or call the Water Team on 01380 736066.