Wednesday, 17 August 2022

Fears over return of river weed

AN invasive river weed that affected water in Wargrave could return in the spring, a villager has warned.

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 growing in the Hennerton backwater in Wargrave in October and also affected the River Thames in Henley and Sonning.

The Environment Agency conducted sweeps of the river to eradicate it but resident Tom Berman says while the weed has been removed, it is still present in the river upstream of Wargrave and landowners and the authorities should be vigilant in case it returns.

The “carpets” of pennywort are too heavy to remove by hand so must be pulled out using mobile cranes then incinerated to ensure they do not reproduce. Every fragment must be destroyed to prevent an infestation from recurring.

Mr Berman, who lives next to the backwater in Henley Road, said: “The agency sent in its contractor, Land and Water, in the first week of February and they spent two days removing every visible patch of floating pennywort along the whole length of the backwater.

“However, because floating pennywort is still to be found upstream in the Thames, we cannot assume that our local problem has been solved forever.

“Fresh pieces of floating pennywort may well float down into the backwater and in the warmer spring weather this weed could easily re-establish itself here.”

Mr Berman said the agency had promised to return to the backwater this month and apply herbicide to any pennywort it finds.

He said: “Longer term, it needs to work with other landowners, including riparian societies, river user groups, residents’ associations and fishing clubs, to eradicate floating pennywort everywhere on the Thames and its tributaries.”

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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