The Environment Agency removed the weed, called azolla, at the start of the summer, but it has such a rapid growth rate, doubling in size every four or five days, that it soon grew back.
Now North American weevils have been introduced to eat their way through the green blanket, which threatens to deoxygenate the water by cutting out light needed by other water plants.
Around 8,000 weevils were introduced into the River Till, a tributary of the Witham last month, in the hope that they would breed and wipe out the weed, after which they should also die away.
Lincolnshire suffered its driest spring for over 20 years this year, prompting the EA to declare an official drought in June after rainfall levels fell to little more than half of their normal amount for six months.
The River Witham was singled out as one of the worst affected in the country, and the weed growth is believed to be related to the warm and dry weather.
For the full story and more pictures, read this week’s Angler’s Mail magazine.