It's often described as an aquatic menace clogging up our waterways and a deadly risk to fish and wildlife.
But the Environment Agency says the threat of floating pennywort has significantly reduced after tonnes of the destructive plant were removed from the River Thames.
Pennywort is an invasive species from North America that can grow really rapidly, in the right conditions with low flows on the river.
In addition to being a flood risk its known to cause problems for navigation, boaters, anglers and can grow by 20 centimetres a day during the summer.
This year the Environment Agency carried out surveillance of over 200 kilometres of watercourse.
They're urging the boaters to be vigilant and to check for signs of the troublesome plant, especially during the winter.