Silage effluent is the suspected cause of more than 1,000 fish dying in a river near Claudy, Co. Derry, according to a statement from the Northern Irish Department of Agriculture, Environment and Rural Affairs.

The incident occurred in a tributary of the River Faughan, and a spokesman for the Department said the Northern Ireland Environment Agency (NIEA) is continuing to investigate a major fish kill near Claudy.

"NIEA was first alerted to this incident on Monday evening and staff have been investigating since then.

“Staff from Loughs Agency, who are leading this investigation, are working closely with NIEA to quantify the number and species of fish affected, and the cause, which is suspected to be silage effluent."

"The latest available figures are that in excess of 1,000 fish of a range of species have been killed over several kilometres of river," said the spokesman.

Staff from the Loughs Agency have commenced electro-fishing and further detailed investigations are ongoing to help narrow the area from where the pollution began.

Meanwhile, NIEA staff are carrying out a river walk to try and find the cause of the pollution.

“If anyone has additional information about this pollution incident they can report this through NIEA’s 24-hour Pollution Hotline (0800 807060),” said the spokesman.

Silage effluent, slurry and milk are some of the most potent causes of waterway pollution on farms, according to Alan Morrow, a Senior Countryside Management Adviser for the Department.

“Dissolved oxygen is essential for a wide range of aquatic life including fish and one of the most common causes of a fish kill is a reduced oxygen supply in the water. The amount of oxygen dissolved in water decreases at higher summer temperatures.

Reduced oxygen carrying capacity often coincides with low summer flows which effectively reduces the potential of a waterway to dilute any pollutants.

"In these conditions, pollution control on the land and farmyards even remotely connected to a waterway must be of the very highest standard to minimise the risk of a pollution incident,” Morrow said.