Thursday, 18 August 2022

Invasive river weed nearly all gone but look out for return

AN invasive river weed is now at “miniscule” levels after more than 40 tonnes was removed from the River Thames in Henley, Wargrave and Sonning.

Floating pennywort, which comes from the Americas, can grow up to 20cm in a day and forms a thick layer that kills flora and fauna by depriving them of oxygen.

The weed was found in the river, including the Hennerton backwater in Wargrave, in October.

The Environment Agency carried out sweeps of the river to remove it.

The “carpets” of pennywort are too heavy to remove by hand so must be pulled out using mobile cranes then incinerated to ensure the plants do not reproduce.

Every fragment must be destroyed to prevent an infestation from recurring.

The agency says there are now only small traces of pennywort left but it will continue to monitor the water as the warm weather helps the weed to reproduce faster. It has appealed to river users to be vigilant and report any sightings.

Biodiversity officer Daryl Buck said: “Our aim is to eradicate floating pennywort from the River Thames completely but we can only achieve this with the continued co-operation of key members of the community.

“Early intervention is the most efficient way to keep on top of this damaging plant as it can grow up to 20cm per day.

“We are urging riverside owners to keep an eye on their watercourse and report any new growth to us. We would also like to hear from river users such as anglers, boaters and canoeists who may come across the plant when out and about enjoying the river.”

Henley MP John Howell said: “The Environment Agency’s surveillance plan needs all of us to report the location of any floating pennywort.

“It is important that we do not simply pass through clumps of the plant as it can break off and spread. I urge those who use the river to be vigilant in helping to stamp out this weed.”

Professor Alastair Driver, an ecologist from Sonning, said: “This is the crucial time now to stay ultra vigilant because the water is warm and this is when pennywort grows back.

“It’s going to be growing very fast over the next few months so we need to keep our eyes open for any fragments and report them to the Environment Agency.

“I’m impressed with the job they’ve done — they’ve listened to what we had to say and responded.

“They now have to try and eradicate every last bit.”

Floating pennywort has broad, shiny, kidney-shaped leaves with fine roots below the water and thick, fleshy stems and occasional small white flowers.

It was accidentally introduced by people discarding garden plants and is thought to have spread to the Thames from a lake at the Green Park science estate in south Reading in 2008.

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