Dead fish have been washed up on the river bank

A mixture of slurry and silage waste, which leaked from a nearby farm into the River Ive, has now spread 12km to the River Caldew.

But Environment Agency officials, who have been battling the pollution around the clock, said preventive measures mean the Caldew will not be affected.

Workers are now searching the river bank for fish, to establish how many have died.

Paul Thompson, from the agency, said it was worrying the leak had doubled in size in just a few days.

'Total wipe-out'

He said: "From the original point it has gone 12km. As it moves down the system it obviously affects more watercourses.

"It reached the River Caldew on Tuesday.

"Thankfully it has been diluted, oxygen levels are back up and it is not affecting the Caldew at all.

"We have had a pump to remove contaminated water to the land and also and aerator to put oxygen back into the water and we are very pleased with the progress."

Mr Thompson added that the pollution could have an impact on fish stocks, but hoped that the fish - including salmon and trout - would recolonize naturally.

He said: "At the moment we have not be able to fully assess the impact. We have fisheries officers attending the becks looking for dead fish.

"Hopefully by the end of the week we will have numbers of dead fish and identify what species are left in the watercourses to see if it has been a total wipe-out or not."