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Guidance on Invasive Non-Native Species

Invasive Non-Native Species (INNS) are those not naturally occurring in specific regions in the UK (non-native) that have been introduced by the actions of humans and rapidly spread, out-competing native species (invasive). Only those that have serious negative impacts on our native species, our health or our economy are considered to be INNS.

INNS and the Thames

INNS are a problem for the Thames and its surroundings with established INNS in the river, on its banks and on nearby land.

The INNS of most concern in the Thames or considered most likely to next invade are listed below. You can find identification sheets, pictures and further information on the GB Non-Native Species Secretariat website.

Common Name Latin Name Habitat Further Info
Water primrose Ludwigia grandiflora Freshwater NNSS Fact Sheet
Quagga mussel Dreissena rostriformis bugensis Freshwater PLA Bulletin October 2014
Topmouth gudgeon Pseudorasbora parva Freshwater NNSS Fact Sheet
New Zealand pigmyweed Crassula helmsii Freshwater  
Killer shrimps Dikerogammarus villosus and haemobaphes Freshwater
Signal crayfish Pacifastacus leniusculus Freshwater
Chinese mitten crab Eriocheir sinensis Freshwater
Pacific oyster Magallana gigas Marine
Veined whelk Rapana venosa Marine  
Marine splash midge Telmatogeton japonicus Brackish  
Carpet sea-squirt Didemnum vesillum Marine  
Slipper limpet Crepidula fornicata Marine  
Japanese knotweed Fallopia japonica Terrestrial  
Giant hogweed Heracleum mantegassianum Terrestrial  
Himalayan balsam Impatiens glandulifera Terrestrial  
Rhododendron Rhododendron ponticum Terrestrial  
Canada goose Branta Canadensis Freshwater
Ruddy duck Oxyura jamaicensis Freshwater
NNSS Fact Sheet
Wakame Undaria pinnatifida Marine  
Pacific wireweed Sargassum muticum Marine  
Pale galingale Cyperus eragrostis Terrestrial  

If you spot one of these species in or close to the tidal Thames, please report when and where to [email protected].

What Can I Do?

  • Report sightings by email with a photo and location details to [email protected]
  • Undertake good biosecurity generally
  • To prevent spread of aquatic invasive species, undertake good biosecurity around water (see GB NNSS Check Clean Dry).

Generic advice for recreational users

Check equipment and clothing for presence of organisms, remove and dispose of safely.

Clean thoroughly, if possible by immersing in 45°C water for 15 mins or hot pressure wash for at least a minute. Contain wash water and dispose of safely.

Dry for at least 48 hours before using elsewhere.

When leaving an anchorage, wash off both the anchor and chain before stowing.

When recovering watercraft, drain water from every part and from all equipment.

Further information available on the GBNNS website

For users of watercraft (boats, canoes, kayaks and all watercraft)

For anglers

For everyone visiting a waterway

For ships – ballast water convention

Why are INNS a problem?

INNS can:

  • Compete with and displace populations of native species
  • Spread disease
  • Clog waterways
  • Restrict navigation
  • Affect water quality
  • Clog water intakes
  • Damage riverbanks and structures

INNS are estimated to cost the British economy over £1.7 billion every year.

What is the PLA doing?

The PLA is co-ordinating the formation of a Thames Vision INNS Working Group. It is planned that the group will produce a Thames INNS Strategy from which an Action Plan will develop to achieve interim targets that will contribute towards the two Vision priority actions to

"improve biodiversity of sites recognised for their wildlife interest and the connections between them" and "improve water quality by a range of measures including reduced litter in the river".


This should help us collectively achieve the Vision Environment and Heritage Goal

"The river the cleanest since the Industrial Revolution with improved habitats and awareness of heritage"

Page updated March 2021.