Freshwater Aquatic Invasive Non-Native Species

Invasive Non-Native Species (INNS) are those that have been introduced (deliberately or accidentally) by people to a place where they do not naturally occur, and have a detrimental impact on the economy, wildlife or habitats.

The Convention on Biological Diversity recognises INNS  as one of the five direct drivers of biodiversity loss worldwide. Many aquatic INNS are not easily visible and are not detected until they are already well established and causing harm. This means it’s important to take measures to prevent their spread, even if you don’t know they’re present.

In Northern Ireland it is an offence to plant, or otherwise cause to grow in the wild, any plant (or hybrid) which is included in The Wildlife (Northern Ireland) Order 1985 (as amended) More recent legislation extends this ban from "in the wild" to include "contained holdings". 

In Scotland it is an offence to plant, or otherwise cause to grow, a plant in the wild at a location outside its native range. The definition of "wild" land is contained in the  Scottish Government's Code of Practice on Non-native species

Examples of freshwater aquatic INNS

North American Signal Crayfish (Pacifastacus leniusculus)

Signal Crayfish have a lobster-like appearance. They are much larger than the native white clawed crayfish. Signal crayfish can grow up to 16cm from the tail to the head. This species is widespread in some parts of England and Wales but is only established in a small number of water bodies in Scotland. It is not found in Northern Ireland.

Signs that Signal Crayfish may be present include burrows in the banks of the water body or parts of dead crayfish on shoreline or banks

Signal Crayfish can destabilise riverbanks through burrowing (burrows can be up to 2 m deep), and impact on native species by feeding on fish and amphibian eggs, young fish and other aquatic species.

Click here to see an image of the North American Signal Crayfish, Image courtesy of GBNNSS.

Asian Clam (Corbicula fluminea)

Asian clam is a small bivalve mollusc, with an inflated shell and is slightly round to triangular in shape. This species is established at a number of sites in England and Wales. It has been found in Northern Ireland but is not present in Scotland.

Asian clam shells can clog water intakes and irrigation channels, and high-density populations in gravels make some building materials worthless. They can alter ecosystem dynamics, increasing sedimentation and competing with native species.

Click here to see an image of Asian Clam, Image courtesy of GBNNSS.

Floating Pennywort (Hydrocotyle ranunculoides)

Floating Pennywort may be free floating or rooted and can grow up to 20cm per day, quickly smothering water bodies. It is widespread in some parts of England and Wales and is found in a small number of locations in Northern Ireland. It has been eradicated from a single site in Scotland.

The estimated cost for control of the total area currently infested by Floating Pennywort in Britain is between £250,000 and £300,000 per year. It can disrupt navigation, damage waterworks by blocking pipes and pumps, or lead to flooding as well as disrupting fishing and other commercial exploitation of water bodies. Dense growth outcompetes native plant species by blocking out light and reducing oxygen in the water.

Click here to see an image of Floating Pennywort, Image courtesy of GBNNSS.

How to prevent the spread of freshwater aquatic INNS

Check, Clean, Dry

Many aquatic INNS are spread through small plant fragments being broken off and washed downstream, or by species being transferred in residues left on equipment or clothing.

Early detection of the presence of freshwater aquatic INNS is important.

Because many aquatic INNS are small and difficult to see, you should always follow the highest standards of biosecurity as a precaution, even if you can't see any INNS where you are working. 

If you or your equipment are in contact with the water environment, the principles of Check, Clean Dry should be followed.

  • Check - Check your equipment, boat, and clothing after leaving the water for mud, aquatic animals or plant material. Remove anything you find and leave it at the site.
  • Clean - Clean everything thoroughly as soon as you can, paying attention to areas that are damp or hard to access. Use hot water if possible.
  • Dry - Dry everything for as long as you can before using elsewhere as some invasive plants and animals can survive for over two weeks in damp conditions.

For more information:

GBNNSS Website Check Clean Dry » NNSS (nonnativespecies.org)

SEPA: Biosecurity and management of INNS for construction sites. 

Biosecurity on development sites and during Controlled Activities

Exercise due diligence by taking all reasonable steps to prevent the introduction or spread of INNS.

  • Assess the risk of your activity causing an INNS to spread (even if they are not known to be on the site)
  • Put in place biosecurity measures such as vehicle washing facilities
  • Brief all contractors and staff so they know what to do

Any pumps and associated pipework used should be:

  • emptied, thoroughly cleaned using a disinfectant approved for aquatic use, rinse thoroughly without allowing the cleaning water to enter the main drainage system (and preferably dried) before it is taken to a site and again before being removed from it.
  • positioned to avoid placing the inlet pipe amongst water plants
  • positioned with the inlet just below the water’s surface, rather than on the bed of the water body.

Read the section on mobile pump operation in SEPAs Good Practice Guide

SEPA: Temporary construction methods 

Further Information

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