Pond plant engulfs Broads waters
The American Floating Pennywort has taken over waterways
The American Floating Pennywort, which grows at up to 10in (25cm) a day, is clogging up waterways and threatens to smother native British plants.
The Broads Authority said the plant had grown over 10,000 sq ft of the River Waveney at Diss in the last few months.
Broads users have urged to inform the authority if they spot any large spanning weeds blocking waterways.
An agency spokesman said it was believed that Floating Pennywort had been dumped into wild waterways from people's garden ponds.