Lincoln residents have been advised to be patient over the water weed still clogging up parts of the River Witham.
The carpet of green weed was triggered by the hot, dry summer.
While it has cleared along the Brayford, the river near the Engine Shed is still looking particularly unpleasant.
Litter can be seen sat on some the islands of sludge.
The lack of rain means that it has linged for longer than usual this year.
The Environment Agency said that the weed will likely die off quickly once the weather starts to turn.
Although they couldn’t give a timeline, they said that cooler temperatures and heavy rainfall will speed to process up.
However, they will step in if it causes problems for wildlife.
A spokesperson for the Environment Agency said: “We’ve had an unusually hot and dry summer which has resulted in prolific weed growth on the surface of our rivers across Lincolnshire.
“Surface weed usually disperses naturally at this time of year as the weather cools and rainfall increases. It’s not been particularly cold yet and despite recent wet weather, river levels are still low so it’s a slower break down than usual.
“If you see fish in distress please report it to 0800 807060.”
It is working with the Canal and River Trust to monitor the situation.
The River Witham in Boston has also been badly affected this summer, with hundreds of fish turning up dead.
Council leader Councillor Paul Skinner recently described it as being in an “appalling state”.
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