The level of access of cattle to rivers and streams can have a significant impact on water quality with implications for human and animal health, according to a new report by the country's main environmental watchdog.
Research commissioned by the Environmental Protection Agency said the negative effect of cattle having access to watercourses was "particularly strong" in relation to levels of bacteria and sedimentation.
It found the impact on the level of nutrients in water was "more variable and site specific".
The report carried out by researchers at Teagasc, Dundalk Institute of Technology, DCU and UCD found increased levels of sediment in streams from cattle acted as "a reservoir for faecal bacteria and phosphorous".
It claimed the problem persisted when cattle were removed periodically from fields with access to watercourses but disappeared when access was prevented on a permanent basis.
"The threat to human and animal health posed by unrestricted cattle access to watercourses and cattle-based agriculture is not confined to the grazing period," the report concluded. It is estimated that between 1.6kg and 2.5kg of faecal matter can be deposited daily in a river or stream per cow.
The report said monitoring data highlighted how increases in turbidity (cloudiness of water), suspended sediment, E.coli, phosphorous and ammonium were recorded when cattle were in a stream.
It is estimated that 73pc of 129,600 farms in the Republic have some watercourse on their lands. River catchments examined as part of the study were the Munster Blackwater, the Douglas in Co Laois, the Bracken in Co Wexford, Milltown Lake, Co Monaghan, and the Commons in Co Louth.
The findings are likely to raise further controversy about the impact of agriculture activity on the environment through pollution of water supplies and greenhouse gas emissions.