Floating pennywort on the Great Ouse

Floating pennywort on the Great Ouse

28 November 2017

IWA is concerned to hear of the increase in the non-native Floating pennywort on the Great Ouse and its tributaries, and encourages boaters and other river users in the area to assist in the Environment Agency’s plans to control the spread of the plant.
 
Floating pennywort (Hydrocotyle ranunculoides) is a species native to North America which was first discovered naturalised in Essex in 1990, having been introduced to the UK as an ornamental plant for ponds.  It is a particular problem for navigable waterways as it can grow up to 20cm a day forming dense mats of vegetation that can affect navigation, angling and water flow, and can increase flood risk.  The plant spreads easily as plant segments break off and move downstream with the flow or get moved by becoming attached to boats, and will continue growing in a new location.
 
Floating pennywort has been a particular concern in the Great Ouse catchment area this year.  Recent mild winters followed by warm weather conditions and low river flows over the summer and this autumn have provided perfect conditions for it.  Growth in the River Great Ouse and Cam has been significant with reports of the plant along much of the River Cam downstream of Cambridge and as far downstream as Denver on the River Great Ouse.   Floating pennywort is also known to be a problem on the River Stort, managed by Canal & River Trust, this year.
 
The Environment Agency has issued a call to boat owners to help reduce the spread of this invasive non-native plant by following the ‘Check, Clean, Dry’ principle - visually checking their craft regularly and removing any visible weed and by placing it well away from any river or other water body.
 
People are asked to report any sightings of Floating pennywort to the Environment Agency via email Anglian-invasive@environment-agency.gov.uk or by calling EA’s national customer contact centre on 03708 506506.   EA is particularly interested in sightings on waterways where it has not been recorded previously so they can monitor the spread and develop a plan of action to combat it.
 
EA states that there is no funding specifically set aside for the control of Floating pennywort on the Great Ouse River system, but they have pulled together an emergency fund of £30,000 and are preparing weed harvesters and other equipment to start removal work on the River Cam.  This is the only funding available at this time and IWA encourages its branches and individual volunteers to get involved with any volunteering opportunities which are organised to help control the spread of this plant.
 
More information about Floating pennywort can be found on the invasive species campaign area of IWA’s website.

Photo: River Cam just below Bottisham Lock, taken 12 October 2017 - The image shows large rafts of Floating pennywort restricting navigation (photo courtesy of the Environment Agency)

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