Article - The River Blog

How to help our rivers… INNS out!

Author: Jeanette Dyson
Categories: Uncategorised

Healthy, well-cared for rivers provide food, shelter and a breeding ground for invertebrates, fish and mammals. In turn, they provide food for larger animals, which is all vital for a healthy, functioning ecosystem.

In our series of ‘How to…’ blogs, we’ll be giving you tips, advice and ideas about how you can help to play your part in keeping our rivers and streams, healthy.

The invasion of non-native species

Invasive non-native species (INNS) are animal and plant species that are not native to the UK. In other words, they’ve been introduced into this country from overseas, either accidentally by stowing away on imports, or purposely, in the case of ornamental garden plants.

Many of these invasive species thrive and spread quickly in our wet, temperate climate and they have a detrimental effect on our native wildlife. They crowd out native species and reduce biodiversity, which Is the variety of plants and animals that an environment supports.

Identifying and controlling INNS

Japanese knotweed, Himalayan balsam, rhododendron, giant hogweed and American skunk cabbage can erode riverbanks and overshadow native plants, reducing the availability of food and habitats for native animal species.

The first job is to identify where these non-native species are located and then to plan and undertake a control programme.

Himalayan Balsam

With its tall stem and pink flowers, Himalayan balsam is a deceptively beautiful plant, but it can wreak havoc on our fragile ecosystems.

What does it look like?

  • Tall plant (can grow to well above head height).
  • Between June and September it produces clusters of pink (in rare cases white) helmet-shaped flowers.
  • Leaves are long and slender with jagged edges.

Where is it found?

It is widespread, but prefers wet ditches, wet woodland and riverbanks It produces pods that burst, scattering up to 800 seeds per plant that can travel up to 7 metres away. These seeds are transported easily by flowing water, which is why Himalayan balsam can quickly colonise river systems.

How can you help?

While difficult to eradicate due to the quantity of plants, Himalayan balsam is one of the easier INNS to handle. Simply pull up and crush the plants before they flower (to prevent them setting seed).

From May to September, we host regular ‘Balsam Bashing’ parties, which are safe for all ages to join in.

Japanese knotweed

Originally introduced in Victorian times as an ornamental garden plant, Japanese knotweed is an invasive plant species that erodes riverbanks and can damage property. It spreads easily and can only be controlled by licensed operatives.

NEVER try to treat Japanese knotweed yourself.

  • What does it look like?
  • It has a green and purple speckled, bamboo-like main stem.
  • Leaves are shield-shaped with a flat base.
  • Leaves form a distinctive zig-zag pattern on the stem.
  • Clusters of small cream flowers appear late July.

Where is it found?

It can grow anywhere. And it grows quickly. It usually spreads via live root (rhizome) or stem material, which is transported in contaminated soil or fragments of the live plant are washed down stream in high river flows.

How can it be treated?

NEVER try to cut or pull up Japanese knotweed. This can cause it to spread. It can be controlled by licensed operatives through carefully spraying or injecting the stems with herbicides. Japanese knotweed can only be disposed of at specially licensed waste sites.

How you can help

If you spot Japanese knotweed near to the River Holme or tributaries, take a photo, note down the exact location and call our team on 01484 661756.

If you spot Japanese knotweed anywhere else, note the location and contact your local council.

American skunk cabbage

This smelly plant prefers wet woodland and can grow up to 1.5m tall, overshadowing native plants.

What does it look like?

  • Bright green leathery leaves that grow in a rosette.
  • Large yellow flowers appear in spring.

Where is it found

It likes wet, boggy conditions, which is why it can often be found close to rivers or in boggy areas that flood frequently.

How can it be treated?

To prevent seeding, remove the flower heads in spring. This does not, however, kill the plant.

Dig out plants with a spade in May or June. Repeat in late summer or autumn if required.

How you can help?

Dig out any plants and dispose of on-site by composting or drying out. Do not leave plants near water or areas liable to flood (as this could help move plant or seed material downstream).

Giant hogweed

This enormous plant has dangerous sap (found in its seeds, leaves, flowers and stem) The sap can cause skin to become photosensitive, causing severe burns and, sometimes permanent scarring.

What does it look like?

  • It can grow to over 3m tall.
  • The stem is thick, bristly and often has purple blotches.
  • Leaves are spiky, serrated and form a rosette shape.
  • The flowers are white and held in umbels (flat-topped clusters).

Where is it found?

Giant hogweed is still relatively rare but becoming more prevalent throughout the UK.

How can it be treated?

Giant hogweed will be treated by specialist operatives wearing full protective equipment.

How can you help?

If you spot giant hogweed, DO NOT TOUCH. If it’s in the River Holme catchment, make a note of the location and contact our team on 01484 661756. Outside our catchment, note the location and contact your local council.

If the sap comes into contact with your skin or eyes wash well with water, stay out of sunlight and seek medical advice.


This popular garden plant spreads quickly in the wild, crowding out native species.

What does it look like?

  • It has long slender leaves with sharp edges.
  • Sprays of reddish orange flowers appear in late summer.

Where is it found?

Montbretia is often found in locations where people dump garden waste. In other words, on grass verges, by rivers, edge of woodland and waste ground.

How can it be treated?

The best way to get rid of montbretia is to dig it out by the roots – which is hard work!

How can you help?

Always dispose of garden waste responsibly at a registered waste site or by using a contained composter.


Our How to… series of blogs is part of our Holme Improvements, year-long project, which is funded by an award from Postcode Local Trust, a grant-giving charity funded entirely by players of the People’s Postcode Lottery.

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