Start with a careful look, not a quick clearance
The Western Cleddau and its tributaries connect riverbanks, farmland, woodland and gardens across Pembrokeshire. Along waterways, some invasive plants can spread through seeds, plant fragments or contaminated soil. Floodwater and routine maintenance can move this material further downstream.
Spotting a suspicious plant early is useful, but pulling or cutting it immediately can make matters worse. The safest first step is to photograph it, note its location and seek identification advice.
The plants below are worth recognising in riverside settings. This is a spotting guide, not a claim that each species occurs at a particular location along the Western Cleddau.
Plants to watch for
Japanese knotweed
Japanese knotweed is a perennial plant with underground stems called rhizomes. Small pieces of viable rhizome or stem material can establish new growth, so careless digging and cutting can spread it.
Look for a combination of:
- Reddish shoots emerging in spring.
- Tall, jointed, bamboo-like stems, often with purple flecks.
- Broad leaves with a pointed tip, arranged alternately along the stems.
- Clusters of small, creamy-white flowers in late summer.
- Dry, standing canes remaining through winter.
Several plants can be mistaken for knotweed, including other knotweed species. Photographs can help with an initial assessment, but a site survey may be needed before planning work.
Do not strim a suspected patch or move soil from around it.
Himalayan balsam
Himalayan balsam is an annual plant associated with damp ground and riverbanks. It can form dense stands, competing with other vegetation. Its seed pods release seeds explosively when ripe.
Useful identification features include:
- Tall, fleshy stems, often tinged red.
- Long, pointed leaves with toothed edges.
- Pink to purplish, hooded flowers, sometimes much paler.
- Seed pods that burst when disturbed.
Because it dies back in winter, dense growth can leave banks with little living vegetation. Management needs to consider bank stability and the plants that will replace it.
Hand-pulling can be appropriate before seeds develop, but only with permission, safe access and a plan for handling the plants. Avoid disturbing seed-bearing stands.
Giant hogweed
Giant hogweed needs particular caution. Its sap can cause serious skin reactions when exposed to sunlight. Do not touch it or attempt to cut it down.
Possible signs include:
- Very large, deeply divided leaves.
- Thick, bristly stems with purple blotches.
- Large, umbrella-shaped clusters of white flowers.
Common hogweed and other members of the carrot family can look similar. Size alone is not a reliable identification test, especially with young plants.
Photograph suspected giant hogweed from a safe distance. Keep children and dogs away. If sap contacts skin, wash it promptly, protect the area from sunlight and seek medical advice; eye exposure needs urgent attention.
Unfamiliar floating plants
Dense mats of unfamiliar vegetation in slow-moving water also deserve attention. Floating pennywort, for example, has rounded, lobed leaves and trailing stems that can form extensive mats.
Do not wade in or rake out an unidentified aquatic plant. Fragments may spread, and water depth, soft sediment and currents create additional hazards. Photograph it from the bank and request identification advice.
How to record a useful sighting
A clear record is more helpful than a bag of plant samples. Stay on public access routes or obtain permission before entering private land.
Record:
- Location: a map pin or grid reference, plus a nearby landmark.
- Photographs: an overview and closer views of leaves, stems and flowers, taken safely.
- Extent: whether it is a single plant, a small patch or a longer stretch of growth.
- Setting: riverbank, ditch, garden boundary, roadside or water surface.
- Risks: proximity to a path, planned excavation or signs that cutting has occurred.
Include the date and say whether identification is uncertain. Avoid walking through the patch. Check footwear and equipment before leaving, removing attached soil and vegetation without transferring them elsewhere.
Who should you tell?
The landowner or site manager
Where ownership is known, notify the landowner or managing organisation first. They can arrange access, assess public safety and coordinate control. Do not begin work on someone else’s land.
For council-managed land or a concern affecting a public route, contact Pembrokeshire County Council through its official reporting channels. A report does not automatically mean the council is responsible for treating the plants.
Records and environmental concerns
Your local environmental records centre can advise on submitting a wildlife record. Recording a sighting helps build knowledge of distribution, but is not the same as requesting clearance.
Natural Resources Wales provides official guidance on invasive species and environmental reporting. Consult it where proposed work could affect the river, a protected site or involve herbicide near water. Check requirements before work starts.
When to call a professional
Arrange a survey when identification is uncertain, suspected knotweed is near planned groundworks, giant hogweed presents a contact risk, or plants extend into water or unstable banks.
Professional help is also sensible where several landowners are involved or previous cutting may have spread fragments.
A sound plan starts with identification and a survey. It should protect existing wildlife, contain fragments, address waste handling and use the lightest effective method. Herbicide should only be considered where genuinely needed and applied by trained professionals, with any necessary permissions. Follow-up checks are often essential; one visit should not be treated as a guarantee of eradication.
Weed Control covers Swansea and West Wales. For help identifying invasive plants or planning appropriate control around the Western Cleddau, call or WhatsApp 07932 064593 to arrange a free survey.