EXPERTS are working to stop a pesticide which has already killed thousands of fish from reaching Colchester.
About 5,000 litres of killer pesticide spilt into the River Colne last Wednesday.
Today it reached the Causeway, in Halstead, killing thousands of roach fish, sparking fears the poison will spread to Colchester.
The concerns have prompted urgent Environment Agency action, including pumping thousands of litres of extra water into the river to dilute the pesticide.
An agency spokeswoman said: “Affects from the spill in Toppesfield Brook last Wednesday are now being seen as far downstream as Halstead on the River Colne.
“We will certainly battle to stop the pesticide from reaching Colchester."
Experts says about 4,000 large fish, including roach, eels, perch and pike and have already died alongside thousands of smaller fish since a farm trailer full of the poison toppled over in Toppesfield on last Wednesday.