Experts winning war on River Nene weed

The River Nene
The River Nene

The Environment Agency is continuing to win the battle against an invasive non-native weed on a Northamptonshire river.

Agency contractors have been out on the River Nene tackling floating pennywort (Hydrocotyle ranunculoides) as part of an ongoing annual project.

Managed by fisheries and biodiversity staff, the project has been carried out every year since 2007.

Using a boat, a powerful aquatic herbicide was carefully applied to the plant by hand along stretches of 17km of the river. A special film was used to make sure the chemical stuck to the plant.

Robert Pitkin, fisheries and biodiversity technical officer, said: “Encouragingly, we noted pennywort was absent from sites where we had previously had large populations. Over the last two years, there has been a 60 per cent reduction in the length of river where we have found floating pennywort - down from 17km in 2010, to 7km in 2012.

“Although some new patches of pennywort were discovered and treated, the number of sites where it can be found has reduced for the second year running indicating that we are keeping on top of this aquatic invader.”

Floating pennywort is native to South America and can quickly establish dense mats of vegetation, out-

competing various native species and completely dominating watercourses. The plant chokes waterways making it difficult for boats to navigate and increases the risk of flooding by slowing water flows and blocking channels. In large quantities, it also poses a threat to fish and other aquatic life by starving the water of light, oxygen and nutrients.

This year’s work to remove the weed from the river cost £2,500 and was approved by Natural England. Works to eradicate the plant have been carried out between Higham Ferrers and Fotheringhay.

Floating pennywort was first spotted on a pond near the River Nene in 2004 but was later found in the river itself, prompting the Environment Agency to begin its eradication programme in 2007. The work will help move the River Nene towards ‘good ecological status’ as required by the Water Framework Directive, a European legislation.

If people do see floating pennywort, which can grow up to 20cm in a single day, it is vital they don’t contribute to its spread. Boats should not be driven directly through clumps of the plant as this can break off pieces which will then re-grow elsewhere. Avoid picking and discarding pieces of the plant as these can grow and colonise new areas.

Anyone who sees floating pennywort should contact the Environment Agency on 08708 506 506 or email