Warning as aggressive fast-growing weed is spotted on the Broads

Floating pennywort - hydrocotyle ranunculoides - has been seen on the River Ant in the Norfolk Broad

Floating pennywort - hydrocotyle ranunculoides - has been seen on the River Ant in the Norfolk Broads. Image: Broads Authority - Credit: Archant

An aggressive aquatic weed that grows up to 20cm a day and can clog up streams and rivers has sparked a warning after it was found the Norfolk Broads.

The Broads Authority has asked river users to be on the lookout after floating pennywort was found on the River Ant, between Tonnage Bridge and Wayford Bridge, near Smallburgh.

The authority raised the alarm about the non-native and invasive species in October, and has now repeated its warning.

Broads Authority ecologist, Jonathan Cook, said the pennywort could end up becoming a major hazard if it is not brought under control.

Mr Cook said: “The pennywort was first spotted in late summer on the North Walsham and Dilham Canal between Honing Lock and Tonnage bridge, but we are uncertain as to how it entered the navigation.

“There’s also a patch at the confluence with the Hundred stream towards East Ruston.


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“It is likely to extend up the stream as well as the surrounding dykes and ditches.

“We are asking people in the area to help out by being on the lookout for the floating pennywort and if they spot it to ensure that they do not disturb it.”

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The weed costs more than £25m across Europe every year to clear up and through lost tourism income.

Floating pennywort is such a successful invader that just a single fragment of it drifting downstream can soon dominate an expanse of water. It out-competes native aquatic plants, blocking out the light they need, leading to the loss of native plants and a sterile river ecosystem.

If the outbreak spreads further it will also affect tourism if dense mats of the plant grow thick enough to block river access for boaters and paddle sports. The plant - whose botanical name is hydrocotyle ranunculoides - has a stalk attached between lobes of a kidney shaped leaf.

People are asked to report any sightings to the Norfolk Non-Native Species Initiative by emailing NNNSI@norfolk.gov.uk, and to stop letting their dogs swim in that part of the river, so the plant is not disturbed and to prevent it spreading further.

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