Weevil wildlife

As we work to bring back more biodiversity along our waterways, our environmental scientist Charles Hughes, is leading a battle to remove invasive, non-native weeds that are taking over our canals. Come with us as Charles, and ecologist Tom King, survey the Shropshire Union Canal for early signs of unwelcome invaders. Find out why this is a fight we all need to play our part in winning.

Before After

“Few people realise that globally, invasive non-native species (INNS) are in the top three threats to our wildlife, alongside climate change and habitat loss,” explains Charles, as we begin our walk. “All around the world, aggressive, invasive species are outcompeting native species, reducing the richness of nature. It’s as big a problem on our canals and rivers as anywhere else.”

That’s why, between now and 2025, Charles is delivering the largest ever INNS eradication project on UK inland waterways. Funded by £600,000 from Severn Trent Water, the project is targeting four invasive plants including water fern, giant hogweed and Japanese knotweed, across 250km of canals and rivers. Today, we’re on the look-out for the other main culprit, called floating pennywort.

“Pennywort grows incredibly quickly, at up to 20cm a day,” says ecologist Tom. “It creates these huge rafts of weed which impedes navigation for boaters and chokes off life in the canals. It outcompetes with other plants for sunlight, reduces oxygen in the water for fish and sucks up all the other nutrients water life depends on. The key is to catch it early, before it blooms in late summer.”

It’s not long before we find some. Every few metres there’s early signs of growth. “We definitely need to do something here,” concludes Charles. “I’ll call the contractors this afternoon.” The main way we manage pennywort is simply lifting it out of the water with floating mechanical diggers. Once large sections are cleared by specialist contractors, we also work with local volunteers and environmental partners to lift out smaller pennywort rafts by canoe. It’s a never-ending, year-round task. But removal is not the only weapon in Charles’ armoury. He says: “Floating pennywort arrived in the UK from the Americas. So now we’ve secured approval from the UK government to run trials with American weevils, which naturally eat away at the plant.” Similar weevils are already showing promising results against the water fern, another invasive species being targeted. Willingness to try innovations like these has now helped the project to win a prestigious award for its impact.

“We’re trying all sorts of things,” Charles enthuses, “from damping down a towpath INNS called Himalayan Balsam with dredged sediment from the canal, to using clay compounds that absorb phosphorus and limit excessive plant growth. We’re also using online mapping tools to monitor weed hotspots, partly to pinpoint what might be causing these blooms in plant life. Are they being fed by run-off from nearby land? Is it more to do with 200 years of sediment and nutrients building up on the canal floor? What effect might more dredging have on reducing problems with INNS? At the moment we just don’t know for sure. But the data from this project is helping us to find out.”

Charles says his collaboration with Severn Trent Water, other environmental partners and consultants from the Netherlands has huge potential.: “We have to tackle invasive weeds like these to give our own native species the chance to thrive. It affects everyone who is responsible for the health of our canals and rivers and everyone who uses our waterways. I’d encourage any boaters, anglers or walkers on our canals to learn to recognise our top four species and use our ‘Clean, Check, Dry’ guidance to help stop their spread. Every small step can help make a big difference.”

Could you help remove INNS from our canals?

Volunteer to help us manage weeds and wildlife canalrivertrust.org.uk/volunteer/opportunities