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Invasive aquatic species

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Our aim is to safeguard, support and encourage both commercial and recreational fishing in Wales.
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Some water plants and animals from abroad can be harmful to our freshwater and marine environments.

Why are invasive aquatic species a problem

Our plants, animals and ecosystems can be damaged by the spread of invasive species from abroad. These species can:

  • block waterways
  • spread disease
  • devastate local plant and wildlife
  • cause economic damage
  • foul hard surfaces
  • damage boat engines.

If you are a water user, you may be helping to spread INNS from one water body to another in equipment, shoes and clothing.

You can help stop this happening:

  • check
  • clean
  • dry equipment before leaving the water.

Our aim

We aim to prevent invasive non-native species (INNS) spreading or being introduced into the marine or freshwater environment and we have a variety of legislation to help with this, such as the Marine Strategy Framework Directive

Due to the dynamic nature of the marine and freshwater environment we can’t always eradicate INNS because it may not be possible or it may be too costly. This is why it is important to prevent their introduction and control the risk of spread. 


We encourage any person working or planning an event in or near the water environment to consider whether biosecurity measures are required to avoid spreading or introducing INNS.

Biosecurity measures include: 
  • following good practice guidance, such as the Marine Check, Clean, Dry campaign, which seeks to prevent the accidental transfer of INNS for anyone visiting or working in or near water 
  • developing a full biosecurity plan which details the specific actions that will be taken to reduce the risk of introducing or spreading INNS. 
Biosecurity guidance is available from the Non-Native Species Secretariat website (external link), as well as identification charts and risk assessments for certain species and a mechanism for reporting suspected sightings of INNS. Free e-learning biosecurity training (external link) is also available.

A priority list of marine INNS has been developed and can be used to help inform biosecurity planning. The list includes INNS which are considered a high or medium risk for Welsh waters and also those which are considered to be invasive but are not currently found in our waters.