UK’s Top 5 Invasive Water Weeds

Jumping across the pond… we may recognize a few watery faces. 

UK’s Top 5 Invasive Water Weeds include a couple North American native aquatic plants.

So we’re kind of on their naughty list. Oops.


While North America has been dealing with non-native plant invasion at every turn, Europe, and specifically the UK, have been battling invasive weeds since the Ice Ages.

Due to its central location and history, the United Kingdom has hosted life forms from every corner of the globe. Whether through humans, trade ships, or melting glaciers, the influx of new organisms has been constant. Consequently, many alien species have naturalized to British ponds and waterways, greatly impacting native plant and wildlife.

Top 5 UK Invasive Water Weeds

Floating Pennywort (Hydrocotyle ranunculoides)

Native to North & South America.

Growing up to 20 cm per day.

Often found in still or slow-flowing water

Impact: disrupts nutrient levels in the water, native plant survival, animal movement, creates erosion and changes water temperature.

It is the most costly invasive aquatic weed found in the UK with an average of €2.5 million annually spent on control.

Recommended Tools: Weed Raker, Swifter Sifter


Parrot’s Feather (Myriophyllum: aquaticum, brasiliense, proserpinacoides)

Native to Central & South America

May continue growing when pond dries out

Grows in a thick mat of vegetation

Impact: In thicker density, can cause flooding by clogging drainways. Flooding increases social and economic costs.

Recommended Tools: Weed Razer Pro, Weed Raker


New Zealand Pigmyweed (Crassula helmsii)

Native to New Zealand & Australia

Can grow on damp land and water

Resistant to frost

Impact: Depletion of oxygen in water known to kill invertebrates such as frogs and fish

Can obstruct watercourse transport and block drainways increasing flood potential.

Recommended Tools: Weed Raker, Swifter Sifter, Weed Razer

Water Primrose (Ludwigia: grandiflora, uruguyansis, peploides)

Native to South America

3 very similar species

Also rampant in France

Contains 2 root systems; one in soil, the other on the linking stem. Broken off pieces may regrow into new plants.

Found in ponds, slow-flowing rivers, farm reservoirs and ditches

Impact: It’s tendency to grow into a thick carpet on the water surface is detrimental to native habitat and species. Also poses flood risk.

Recommended Tools: (depending on density) Weed Razer Express/Weed Razer Pro; Weed Raker

Water Fern (Azolla filiculoides)

Native to tropical Americas

Known as fairy fern. Turns brown in autumn.

Floating fern forms a dense mat with hanging roots

Grows and doubles its mass in 2-3 days

Transported on other plants as hitchhikers

Impact: Dense mats decrease oxygen levels in water, when transported on other plants can act as contaminant.

Recommended Tools: Swifter Sifter; Weed Raker


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