Photos of the spill on the Ballinderry River.
A section of a County Derry river has been hit with a second slurry spill in less than a month.
The lower reaches of the Ballinderry River, stretching between Coagh, Co Tyrone and the Ballinderry Bridge has been affected.
At the end of March, a slurry spill on the same river caused 'devastating' damage, with thousands of fish killed by the spill, which the local council said was 'self-reported'.
The Ballinderry Rivers Trust has said the latest incident was spotted by a member of the public.
"The Ballinderry River has been hit with slurry pollution again," they said via their official Facebook page.
"This time in the lower reaches of the river between Coagh and Ballinderry Bridge. The Trust alerted NIEA following a report of slurry in the river by a local concerned river user.
"Thanks to their swift action pollution officers were able to collect samples.
"Early indications suggest that this slurry entered the river during the night and the volumes involved are not what you would see from slurry being spread in a field too close to the river.
"Thankfully there is no reports of dead fish and the NIEA investigation is ongoing.
"Slurry should not be in rivers. This reckless polluting of our rivers and Loughs has to stop."
Subscribe or register today to discover more from DonegalLive.ie
Buy the e-paper of the Donegal Democrat, Donegal People's Press, Donegal Post and Inish Times here for instant access to Donegal's premier news titles.
Keep up with the latest news from Donegal with our daily newsletter featuring the most important stories of the day delivered to your inbox every evening at 5pm.