Wild Swimming With Penny Wort

Gillian Branson

In mid-September, I donned my drysuit and floated on my first wild swim of the year in the upper River Arun near Horsham. My company was Penny Wort who hails from North America, with representatives from Horsham District Council, Friends of Chesworth Farm and the Environment Agency.

We were there to send Penny on her way. She shouldn’t be there. Although we’re always shouting about increasing biodiversity, this requires a balance between the number of different species (richness) and their abundance. When one species demonstrates incredible speed and spread of growth it can outcompete other species, blanket the area and reduce biodiversity and habitat quality. This is particularly prevalent in species brought in from other parts of the world to go into our gardens and ponds that easily escape but are not limited by our climate or habitats. We call these invasive non-native species (or INNS). You have probably all seen large stands of Himalayan balsam with its lovely pink flowers and its juicy smell of rivers and, much like the rhododendron effect, you probably love them. But they are invasive and can take over a large area of river bank, restricting other species and reducing cover when they die back to nothing in the winter, leaving the river bank exposed to erosion during winter floods and rainfall run-off.

Penny, I’m afraid, is also invasive, she won’t take no for an answer and simply has to go. She is known as floating pennywort and can root in soft muds or attached to tree stumps or roots, and will float on the surface covering very large areas, the whole water surface if left alone. The largest stand we saw here was the size of two king-size beds with many smaller stands floating around further downstream. They spread vegetatively and can set seed so need to be physically removed to keep their effect minimal. Although banned from sale in 2014, it can often be mis-sold as our native marsh pennywort or as water pennywort.

We (the Arun and Rother Rivers Trust or ARRT) are on the site at Horsham District Council’s Chesworth Farm to improve fish passage, habitat condition and water quality to support improvements under the Water Framework Directive (WFD), but we saw the great opportunity to make a dent in the stand of one invasive species and worked with our partners to make it happen. This is near the top of the catchment too so should reduce the speed at which it will recolonise. There are already some patches downstream and it needs a concerted effort to remove all of this and the many other INNS in the catchment.

Our RAINS initiative (River Action on Invasive Non-native Species) aims to build a support network of volunteers (River Squads) to help in spotting and removing INNS and to use scientific and technological efforts to monitor their spread, such as drone surveys of areas within Local Authority boundaries, and the use of environmental DNA (eDNA) to track progress of their eradication.

I thoroughly enjoyed my wild swim and will look for other locations in the Arun once we’ve cleaned it up a bit. Any suggestions welcome!

Do get in touch with us if you would like to be involved in any of our initiatives or would like some advice. You can contact us HERE

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