Doing More for the Derwent

INNS Control

Background to project

The Yorkshire Derwent is the largest single river catchment in Yorkshire. It has its headwaters in the North York Moors and flows south from there through the lowlands of the Vale of Pickering and Vale of York to its confluence with the River Ouse at Barmby Barrage.

The main River Derwent flows through many important designated areas and is itself a Site of Special Scientific Interest (SSSI) for 86km due to its nationally significant fauna and flora.

Yet the River Derwent suffers from environmental pressures including Invasive Non-Native Species (INNS). Numerous alien species have been recorded in the catchment, most notably; Himalayan balsam (Impatiens glandulifera), giant hogweed (Heracleum mantegazzianum), Japanese knotweed (Fallopia japonica) and orange balsam (Impatiens capensis).

In 2017, the Environment Agency commissioned the Yorkshire Derwent Catchment Partnership (YDCP) to create a catchment-wide strategy to tackle riparian plant INNS. From the available data, the distribution of these non-native plants was mapped out, along with priority treatment areas. A top-down approach was developed for treatment to ensure treated areas would not become re-infected from waterbodies upstream.

Through the Environment Agency’s ‘Doing More for the Derwent’ project, looking to enhance and restore the ecological health of the River Derwent SSSI, INNS work has been carried out over the past 3 years by the partnership’s host organisation, Yorkshire Wildlife Trust.

Our targets



Map key invasive non-native plant species (giant hogweed, Japanese knotweed and Himalayan balsam) within the catchment and monitor annually.


Eradicate two sites of monkey flower (Mimulus luteus).


Reduce giant hogweed by 50% coverage within the catchment and eradicate orange balsam.


Giant hogweed will be eradicated from the catchment and Himalayan balsam reduced to 30% of the 2018 area

Progress so far

The primary focus of our treatment plan is the eradication of giant hogweed. It is notable for its large size, towering over other herbaceous plants, and impressive umbel flowers. This species out-competes native flora and has a fearsome reputation for causing burns on human skin, caused by its phototoxic sap. YWT staff and trained volunteers have carried out spraying and stem injection of giant hogweed over the past 3 years, mainly in the middle Derwent where the infection is the most severe. Himalayan and orange balsam pulling is also carried out by volunteer groups in priority areas. There is also a small amount of Japanese knotweed on the SSSI that is being treated each year.

Landowner Pay-In Approach

Having successfully established a landowner pay-in scheme on the River Colne in West Yorkshire for Japanese knotweed, Yorkshire Invasive Species Forum (YISF) were contracted to trial this for Giant hogweed on the River Derwent and Bugthorpe Beck in 2019. Through the giant hogweed pay-in scheme, 32 landowners were engaged with, and 2500m² of INNS were treated. There are plans to expand the pay-in scheme in future years to encourage land owners to control INNS on their own land, and reduce the reliance on external funding to prevent the spread of INNS.


Trained volunteers have been busy across the Derwent catchment, surveying areas where there is little or no INNS data, this is vital to help us update our control strategy and carry out more effective treatment.

So far 192km of watercourse has been surveyed by YDCP through staff and volunteer efforts.


Good biosecurity is of significant importance in the catchment particularly in areas where there are vulnerable species such as white-clawed crayfish. We adhere to strict biosecurity procedures when working in the catchment to protect what is there and prevent the spread of INNS and other harmful species between sites. Throughout all work undertaken, YDCP carries out biosecurity procedures based on Yorkshire Invasive Species Forum’s best practice guide.

Partner activities

Partner organisations working within the Derwent catchment have primarily focused on tackling Himalayan balsam. NYMNPA have started delivery of Himalayan balsam control as part of their 4 year Ryevitalise scheme which includes projects addressing both plant and animal INNS. The Howardian Hills Area of Outstanding Natural Beauty (HHAONB) has been controlling Himalayan balsam on keys sites, particularly locations designated as a Site of Importance for Nature Conservation (SINC).

Key achievements

How can you help?

We are always looking for enthusiastic volunteers to help with our work. If you are interested in training to be a INNS surveyor on the Derwent catchment, please contact

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