An ambitious new project is being led by the Colne Valley with the aim to clear the River Colne running through Denham Country Park of the invasive species Floating Pennywort. Floating Pennywort is a plant, originally from South America, that has invaded rivers throughout England. Floating pennywort forms large rafts on the surfaces of waterbodies, composed of many crinkled kidney shaped leaves and tied together with stem and root systems. These floating pennywort rafts drive a range of negative environmental impacts on rivers. For instance, Floating Pennywort reduces the amount of light that reaches the river, meaning that other aquatic vegetation cannot grow. Additionally, floating pennywort, due to its rapid growth rate of up to 20cm a day, consumes lots of Oxygen present in the river, which can lead to deoxygenation of the river that drives reductions in aquatic wildlife populations which can no longer survive. In severe cases, where floating pennywort is left unmanaged and grows to cover the whole river, it can increase local risk of flooding due to slowing water movement. Floating Pennywort also prevents recreational use of water bodies and causes navigational problems due to blocking up rivers with vegetation.
Large rafts of Floating Pennywort are currently present in the River Colne, however there are plans to tackle this invasive plant and improve the river Colne! The Rivers Team at Colne Valley have been conducting preliminary surveying for a project funded by HS2 via Buckinghamshire Council. This work has involved conducting a survey of the whole area of the Colne for both floating pennywort and protected species. This data is incredibly important for ensuring we can focus our removal work, completely remove all this plant from this area and monitor the extent of any future infestations in comparison to before the removal works.
Recent survey showed Floating Pennywort visible in Denham Country Park.
The protected species surveying, and collation of previous surveys highlighted how important much of this area around Denham Country Park and the River Colne is to wildlife. This river is a common migration route for trout and eels, as well as recent sightings of water voles, otters, kingfishers and many protected ground nesting bird species. Due to these species being present, all removal work will be conducted from boats, to minimise the effects on protected species in the area whilst still conducting river improvement work and the removal of invasive species.
The removal of the floating pennywort from the river Colne is planned to occur either October this year or March 2025, depending on weather conditions. We will be following up the first round of removal works with monitoring and any further small fragments that colonise or regrow will also be removed. So, keep an eye out for floating pennywort removal on the river in Denham Country Park, and hopefully you will be seeing a river clean of this floating plant soon!
If you would like to help us in the fight against the Floating Pennywort please get in touch with our Rivers team [email protected]
Lara Clements who is leading on the river improvement work
