Invasive plant species eliminated on a 10 km stretch of the Cam River

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An invasive species was cleared from a stretch of the Cam River by volunteers this week.

A 10 kilometer stretch of the river between Byron’s Pool and Jesus Green Lock is now pennywort free and the threat of losing the river to this invasive species has passed.

The Environment Agency, supported by volunteers from Cam Conservators, used weedkiller boats to remove floating pennywort, an invasive non-native aquatic plant that had formed thick mats along the river.

It was growing at a rate of eight inches per day, which meant that the return channels were lost, navigation for boaters and canoeists was difficult, and the impact on wildlife and plants was significant.

Pennywort can alter the availability of oxygen in the water, threatening fish and invertebrates. It can also clog drainage systems and clog native aquatic plants.



Pennywort covering the river before the volunteer work

Mike Foley, a retired Cam Valley Forum volunteer who has spent years fighting the invasion, was one of the people who went “above and beyond” to rid the river of pennywort.

Over the past year, he worked even harder to keep the momentum going when group meetings were difficult to coordinate.

Mike said: “It’s great to see this stretch of the River Cam free of pennywort.

“Once you start removing this invasive plant, it’s impossible to stop because you just want to see the job done.

“I want to thank everyone who got involved and helped us along the way. This project is proof that hard work pays off and that we work better together. “

Anne Miller, a volunteer who worked closely with Mike, helped raise funds so they could prune two miles of overhanging branches.

This allowed them to remove the pennywort that was trapped, which was essential for the removal of the invasive plant.

Anne said: “I was saddened to see the river above Cambridge get clogged with this overwhelming weed and I was inspired by Mike to start fighting it.

“There were hundreds of tons of material to be removed and the pennywort was tangled in the branches of the trees, so I thought we needed help.

“With funding from the Environment Agency and others, I hired contractors who did a brilliant job removing fallen tree branches on a two mile stretch above Cambridge. This type of partnership is very satisfying. “

Floating pennywort is difficult to control and eradicate as it has the ability to grow back from a small shard.

This is why constant monitoring of the sections of the river where the pennywort has been removed is necessary.



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The plant was introduced to the UK aquatic nursery trade in the 1990s, but its sale was banned and its planting was banned in 2014.

James Brokenshire-Dyke, Project Engineer at the Environment Agency, said: “Mike went out of his way to clean up the pennywort.

“He digs and picks the plant by hand, he takes many walks to check that it hasn’t regrown, and talks to various people to raise awareness and much more.

“Without it, pennywort would have spread further and we wouldn’t know of new outbreaks. Mike’s work is invaluable to us, as is the work of all the volunteers who have contributed.



Volunteers attacking pennywort

Tom Larnach, River Director at Cam Conservators, said: “Working with Mike and the volunteers has been great, we’re just a small team so we really appreciate all of their help.

“This project has been a good example of a partnership. Normally around this time of year we start to see pennywort rugs forming, but I haven’t seen a single one.”

Members of the public can stop the spread of this invasive species by recording any sightings on the iRecord app.

Boaters and other users can also help by checking equipment and clothing for living organisms; thoroughly clean all equipment and clothing with hot water; and thoroughly dry all equipment and clothing, as they can live days in humid conditions.

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