Source to Sea

In 2012 the Environment Agency, Wiltshire Wildlife Trust, Hampshire and Isle of Wight Wildlife Trust and Dorset Wildlife Trust formed the Source to Sea Project to remove non-native invasive species from the entire length of the Hampshire Avon. Plants such as Himalayan balsam, Japanese knotweed, giant hogweed, water fern and creeping water primrose will be targeted, and the catchment will be closely monitored to quickly recognise and respond to any new pests that may appear. The project covers the whole of the River Avon catchment from its headwaters in the Vale of Pewsey, down through Salisbury into Hampshire, to where it meets the English Channel at Christchurch Harbour.

Our Aims

  • To deliver management, control and eradication of priority invasive non-native species in Avon catchment.

  • To work to establish a self-sustaining network of public and community support, leaving a legacy after the project.

  • To develop a reporting procedure for the early detection, surveillance and monitoring of new species.

  • To publicise and encourage biosecurity best practice.

  • To evaluate the effectiveness of the catchment scale approach and share lessons learned nationally.

  • To monitor and evaluate different removal methods and share lessons learned nationally

  • To support the feasibility assessment of any relevant biological control programme, and consider Avon catchment as a potential test site.

Source to Sea catchment map

Leaflet with further information

Quarterly report April/June 2012

Water Fern completely smothering this water body south of Ringwood

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.


In previous projects we have tended to focus on the ‘big three’ problem species; Himalayan balsam, Japanese knotweed and giant hogweed. Hampshire and Isle of Wight Wildlife Trust, one of the partners in the Source to Sea project, have experience in dealing with other less well known invasive plants. Most of these species have not yet taken hold of our rivers so it is vital that we act now to ensure they never have the chance to spread.


Parrot’s feather, American skunk cabbage, creeping water primrose and New Zealand pygmyweed are examples of the other species we are tacking over the course of the project. Even though they may not be present in the same quantity as Himalayan balsam, in many ways they are more difficult to control. Most grow in the water, at least partly submerged, making it very difficult to control with herbicides. We will not give up however and will be providing on-going updates on our progress.

One of the contractors spraying giant hogweed at Wilton, on the Nadder (left), and the same Wilton site showing giant hogweed dieback, after herbicide treatment (right)


As a catchment project we have found it easier to convince landowners that it is worthwhile investing money in invasive plant control. This year we have developed and implemented Memorandums of Understanding, with two large estates, which detail committed financial contributions for giant hogweed treatment, from both Source to Sea and the landowner, over the next 3 years. Our contractors have struggled to find a suitable window to spray because of the combined bad weather and high flow levels, but eventually we did manage to complete all of the spraying planned for this year. The chemical used is approved for use near water and early monitoring is indicating that the treatments have been successful.

An extensive programme of volunteer tasks was run between May and September of this year, for the purpose of Himalayan balsam removal. Adverse weather conditions and high flow levels have impacted upon both volunteer numbers and our ability to run tasks safely, but we still managed to successfully remove Himalayan balsam from over 35 kilometres of river bank.

Source to Sea Field Officers started multi-year treatment programmes for Japanese knotweed, in the catchment, in 2012. Stem injection guns are used to deliver herbicide into the stems of the plants, with treatment occurring between September and October; which follows on nicely at the end of the Himalayan balsam pulling period. This year we treated Japanese knotweed equating to an area of 286m2.

The River Avon’s Army needs more volunteers

Volunteers for the Source to Sea project recently gathered for the Annual Meeting. View the press release here.





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