Tackling a non-native invasive species
Volunteers from the Canal Society have been working in cells of 6 clearing the surface weed between the junction of the canal and River Wey and up to lock 3 at West Byfleet, and in parallel they have been working downstream from lock 7 to Woking Town Wharf – and the reason?
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 now is pervasive in the Woking area from the junction with the River Wey though to Lock 7 (Langmans Bridge).
It is a particular problem for navigable waterways and canals are particularly susceptible, as the plant grows quickly in the slow moving, nutrient rich, warm water. The weed can grow up to 20cm a day forming dense mats of vegetation that can affect navigation (stopping canoes and paddleboards as well as hindering powered vessels), angling and water flow, and can increase flood risk.
Once the plant takes hold it can cost thousands of volunteer hours to remove and dispose of. It will completely dominate an area, so that nothing else can survive (as it blocks out sunlight and oxygen), potentially degrading this important SSSI.
The team have been assisted with the BCA weedcutter (top) crewed by the BCS volunteers and this can take out the large mats in one go (maybe 250 kg), but most of the time the team are using canoes to place grappling hooks on the mats and pulling them into the bank for removal. Bear in mind that most of the weed is just water, so the teams are pulling out tonnes of stuff on every visit – who needs a gym!!
At the time of writing we still need to clear the section from Woking Town Wharf down to the top of Lock 3, and we know that in some areas the canal is completely covered by the weed. Almost analogous to painting the Forth Railway Bridge a never ending task!!