Skip to main content

The charity making life better by water

Green invasion tackled on London's waterways

A peculiar phenomenon is appearing on London’s canals, as a spreading carpet of weed attempts to turn hundreds of metres of water green.

Duckweed on canal

We have special ‘weed-eater' boats out on the water to scoop up millions of pieces of the floating duckweed.

It's naturally occurring and multiples rapidly in the warmer temperatures. It can double in size over a matter of days so we're working to prevent the city's waterways being taken over.

This week alone, around ten tonnes of duckweed have been collected. It comes at a time when more people than ever are visiting London's canals to relax and chill out, with thousands boating or using the towpaths each week during the summer.

While an individual piece of duckweed is no bigger than a ladybird, they grow together to form a carpet across the canal. This traps litter which, as well as looking a mess, can cause problems for boats and leisure craft on the water.

The weed is not harmful to people, but dogs and other animals have been known to mistake it for grass and ended up in the water. Significantly, if left to thrive, it can cause problems for other aquatic wildlife by starving the water of oxygen and sunlight.

Sam Thomas, the Trust's customer operations manager, says: "Duckweed is a real challenge on the canals at the moment and with more hot weather on the way, it's going to continue growing. It grows so rapidly and is tricky to collect because the individual pieces are so tiny.

"We use special boats to keep on top of it but, with the movement of the water, it's a bit like trying to mow a moving lawn. The weed itself isn't harmful – in fact lots of ducks, geese and some fish like to eat it – but it looks bad, traps rubbish, and it can cause problems for boaters too."

We are urging people to take care when out walking with dogs and with their families, and asking people not to throw litter onto the weed.

Two women eat lunch next to the canal

Wellbeing on your doorstep

Find somewhere beautiful to rest, relax and recharge. Discover what's local to you

Kingfisher in flight with small fish in its beak

Support our work

We need your support to keep canals and rivers alive. Donate today to make a difference

Last Edited: 21 June 2018

photo of a location on the canals
newsletter logo

Stay connected

Sign up to our monthly newsletter and be the first to hear about campaigns, upcoming events and fundraising inspiration