Inland Fisheries Ireland is appealing to farmers across the Shannonside Northern Sound region to protect watercourses during the silage season.
The semi-state body is advising farmers to follow its six-point SILAGE plan for optimum silage and slurry spreading etiquette to reduce the risk of polluting rivers and lakes.
Linda Connor, the South Eastern River Basin District Director, pointed out this week that if effluient enters water courses, oxygen will become depleted and contribute to a fish kill.
She said IFI's SILAGE plan would help farmers and food producers to eliminate contamination of local water sources.
Ms Connor added that if people notice anything suspicious in their area, they should contact IFI immediately.
"If the nutrients are too high, whether its nitrates or phosphorus entering the water, it can deplete the oxygen levels and put the fish under pressure, especially the more sensitive and intolerant species like salmon or trout. The message we'd like to get out today is that if anyone comes across anything like this we would encourage them to ring our confidential hotline on 0818 347424".