Aquatic and riparian weeds

These pages are under development.

What is the issue with aquatic plants?
Some plants which are not native to Britain can become invasive when they are introduced to the wild.  They can grow very quickly, even from tiny fragments – for example Floating Pennywort can grow up to 20cm a day.  Once in the wild, they overgrow habitats and other native plants and can form dense mats in the water which reduce light and oxygen levels in the water which harms fish and other natural life.  They can be very difficult and expensive to control.  These plants often don’t make a very good choice for garden ponds as they overgrow them quickly and need a lot of management.  

What are the economic implications of the problem

Once established, invasive plants can be very difficult and very expensive to control.  It is estimated that the Environment Agency spends approximately £1.5 million a year on invasive aquatic plants due to the flood risk they pose. British Waterways spend about £1 million a year on invasive non-native species (including riparian – riverbank – species). Floating Pennywort is currently thought to be the most expensive aquatic weed, it is estimated that it costs over £2.5 million each year in control, and its impacts on leisure, recreation and flooding. Water Primrose could be just as bad but we have acted quickly to try to stop it from establishing in Britain.  

Are we saying all gardeners shouldn’t have these plants in their ponds?

No – providing they don’t escape into the wild it is fine to have INNS in your pond, though they may not be suitable due to their fast growing nature. The important thing is to make sure that unwanted plants are disposed of properly so that they can’t get into the wild where they cause problems.  

How should people dispose of them properly and what guidance exists on this?

If you have an invasive species in your pond and you manage it correctly there’s no problem. If you decide you don’t want it any longer then you should make sure you dispose of it safely so that it can’t get into the wild.  They can either be composted in the garden or by using your local green waste disposal scheme. Before composting, plants should be left to dry out beside the pond so that any pond animals in the plants can return to the pond. Make sure you get every last fragment as new plants can grow from the tiniest piece.   Plants can be pulled out on a regular basis, but any big clear out should be saved for autumn when it will cause the least disturbance to the pond.  It may be best to take advice if your pond flows into a stream or other body of water to make sure you don't accidentally spread the plant into the wild.  

If I spot a harmful plant in a public waterway, what should I do?

Many of these plants are fairly widespread in the countryside.  You can find out more information on these species on the Be Plant Wise pages including handy identification sheets for several key aquatic species and their current known range. You can submit records of non-native species through the online recording scheme iRecord (external link). Read more about recording non-native species. Some species – such as Water Primrose – are not so widespread and it would be useful to know if they are present in other areas. There are a number of volunteer groups that clear non-native species from waterways that you could also notify of the problem. Read more about local action groups in your area.

Why are you majoring on these five aquatic plants?  What alternative plants do you recommend?
These top five plants are all causing major problems in the wild.  They have a number of impacts including:

  • outgrowing native plants,
  • interfering with activities such as angling and boating, 
  • clogging waterways and exacerbating flooding,
  • reducing light and oxygen levels in the water which can harm fish and other creatures,
  • forming thick mats which can look like dry land and can be a danger to people and livestock.

There are many other aquatic plants available to buy that will still oxygenate your pond, provide shelter for pond creatures or produce lovely flowers. Plantlife and the Royal Horticultural Society have produced three guides to plants that you could use in place of harmful invasives. You could also ask your retailer for advice about choosing plants which are suitable for your pond and not likely to cause a problem for the environment.

Can I join a volunteering group to help clear public waterways?

There are many projects around the country that are tackling invasive species in their local areas.  Read more about local action groups in your area.  Otherwise try contacting your local authority, the nearest offices of the Environment Agency or Natural England, your local Rivers Trust, Wildlife Trust, the National Trust, British Waterways and so forth. 

What can the public do to help and where can I find out more information
The public can help in many ways.  For example heed advice on buying, using and disposing of invasive aquatic plants; make your friends and relative aware of the issue; check the website for information and handy identification sheets for key invasive species and report them if you find them; volunteer with local action groups in your area to help manage the problem locally.  


What are the penalties if people introduce these into the wild? 

Information on legislation.

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