This is obviously a very serious incident and the impact on the Gadie Burn and the River Urie will be significant

Stewart Mitchell, Sepa

But Sepa's Stewart Mitchell predicted that there would be a "significant" impact on Gadie Burn and the River Urie.

Environmental protection officers were continuing their probe into the cause of the spillage into the Gadie Burn near Oyne on Thursday afternoon

The environmental watchdog was immediately alerted as the burn is a tributary of the River Urie, which in turn runs into the River Don a few miles down stream at Inverurie.

The main A96 Aberdeen to Inverurie road was closed for several hours between the Oyne fork and Colpy.

The slurry sucks oxygen from the water, which threatens valuable fish stocks.

Accidentally discharged

A farm close to the site was fined �500 after up to 200 young salmon were killed when 5,000 litres of slurry was accidentally discharged in July last year.

Salmon fishermen said they would be seeking compensation after this latest incident.

Jim Kerr of the Don Salmon Fishing Board said it was "a major disaster", especially at a time of year when salmon and trout were spawning.

He said: "This salmon is going to wipe out adult salmon and adult trout. It's a disaster."

Hay bales were used to stop the slurry

Hay bales and earthwork barriers were used in an attempt to minimise the amount of slurry entering the watercourse.

Mr Mitchell said: "This is obviously a very serious incident and the impact on the Gadie Burn and the River Urie will be significant.

"Sepa officers responded quickly but the causes of the discharge are still under investigation.

"In these circumstances, if appropriate, enforcement action may be taken."