Thousands of brown trout and salmon died on a 12-mile stretch of the Ballymartin River and Sixmilewater between Mallusk and Antrim after a pollutant entered the watercourse on Friday.

EHS staff were tasked to the Sixmilewater on Friday evening following reports of a heavy foam moving down the river near Templepatrick.

On Saturday morning the extent of the damage to the watercourses was becoming apparent, with hundreds of dead fish being reported by members of Antrim & District Angling Association (ADAA).

Fishery Manager Allan Kirkpatrick commented: "I counted 1,837 dead fish myself and that was only on part of the river. Over the 12-mile stretch we're talking many thousands of dead fish, not to mention the effect this will have on all the wildlife such as the otters and kingfishers that live along the river.

"It's killed everything in the Ballymartin and everything from where the Ballymartin enters the Sixmilewater near Templepatrick right as far as Antrim.

"The Ballymartin River is being polluted 24/7 with various chemicals and oils and it's an absolute disgrace that this is allowed to happen in this day and age. It's an environmental disaster."

Mr Kirkpatrick said that EHS need to be given more resources to help them deal with the ongoing pollution problems in the Ballymartin River, adding that tougher penalties need to be handed out to those found to be responsible.

The same 12-mile stretch of river was the scene of a major pollution incident in 2006, and local anglers are furious at this latest fish kill.

"The Association had just completed major enhancement works at the end of last year and the resulting increased productivity will have been negated as all spawning beds and food supplies over this stretch of waterway will have been poisoned," said ADAA Chairman Paul Erwin.

"At best someone's gross carelessness, and at worst someone's wish to save a few pounds on waste disposal, has caused and will continue to cause the wildlife along the Ballymartin Water and Sixmilewater suffering and death," he added.

An EHS spokesperson confirmed that a sample of the foam discovered on the river was taken for analysis, but said that the results won't be available until the end of the week.

The investigation involving EHS officials and the Fisheries Conservancy Board, which is understood to be centering on premises in the Mallusk industrial area, is continuing.