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Waterways Battle Against Alien Invader

British Waterways and the Environment Agency have combined resources to tackle a growing problem on Yorkshire’s canals and rivers this week, after coming under threat from an ‘alien invader’ – an invasive weed known as Floating pennywort or Hydrocotyle ranunculoides.

Supporting last week’s announcement by Defra on its Be Plant Wise campaign, which aims to raise awareness among gardeners, pond owners and retailers of the damage caused by invasive aquatic plants, British Waterways North East Region is stepping up its fight to stop the spread.

Sprotbrough along the River Don in South Yorkshire, the Figure of Three Locks in Horbury on the Calder & Hebble Navigation and isolated locations on the Aire & Calder Navigation around Castleford have all been struck by aquatic weeds costing more than £50,000 regionally per year. Nationally British Waterways spend more than £350,000 in aquatic plant removal annually.

Floating pennywort, a native species of North America, was brought to Britain in the 1980s as a plant for tropical aquaria and garden ponds. By 1991 it had become present in the wild and has since found its way onto parts of the inland waterways network from people releasing them from their ponds and aquariums. The weed roots in shallow margins of slow-flowing water, particularly in canals, rivers and lakes, as well as ditches and slow-flowing dykes. If left unchecked it can form thick mats, starving waterways of sunlight and oxygen and interfering with boating, angling and wildlife.

With growth potential of up to 20cm per day and the ability to regenerate from the smallest fragment, control of the weed can be extremely difficult and expensive. If not tackled properly, it can cause a range of problems including: choking drainage systems, crowding out native water plants and taking oxygen from the water that is vital to the survival of fish and insects.
Jonathan Hart-Woods, Environment Manager for British Waterways said: “Floating pennywort demands ongoing monitoring and intensive action to control it as it can spread at such an alarming rate. To be effective we need to mechanically dig out the weed, as well as using a licensed herbicide to kill the weed to try and prevent the spread as much as possible. However, this is not easily achievable due to its ability to grow from fragments as small as 10mm in length.”

Floating Pennywort isn’t the only plant which is putting a strain on the waterway system. Other highly invasive plants include Japanese Knotweed (Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica), Himalayan Balsam (Impatiens glandulifera) and Giant Hogweed (Heracleum mantegazzianum, aka giant cow parsley).

Jonathan continues: “This is the International Year of Biodiversitiy so BW are determined to make a real difference and ensure a more effective approach to the management of these plants, despite the difficulties of effectively controlling the spread. This is becoming a big issue for the waterways and one that we can’t afford to be complacent with. The allocation of already stretched resources between partners such as the EA, Angling Groups and Local Authorities has been essential for its success and demonstrates our ongoing commitment to protecting the ecology of the waterways.”

Andrew Virtue, Environment Agency biodiversity officer, said: "Pennywort has only really arrived in Yorkshire in the past couple of years. At present, it is known to be in South and West Yorkshire - we are currently surveying its extent and need to remove it before it spreads further. Other invasive species such as Himalayan balsam and Japanese knotweed are so well-established that they are virtually impossible to eradicate, and we want to tackle pennywort before it can become as big a problem."