EXOTIC plants thrown away by their owners are overwhelming Britain's rivers and canals.

Floating pennywort and giant hogweed damage wildlife, boating, access to banks and towpaths and maintenance of locks, bridges and channels, say British Waterways.

Dealing with the problem costs the organisation, which manages 2,200 miles of canals and navigable rivers, around £1m a year.

It urged people to think twice before buying non-native plants for ponds and gardens which could escape into the wild. Gardeners should dispose of unwanted plants responsibly - and not throw them into waterways or over the garden fence.

Chris John from British Waterways said: "Many non-native species pose real problems to our native wildlife, to boaters and to our historic channels, locks and bridges.

"With no natural predators to control them they can overwhelm wildlife, channels, banks and towpaths."