Bathers are being advised not to swim at Lough Muckno due to an increase in levels of bacteria found in a sample taken at the popular Castleblayney amenity.
Samples taken at the Lough Muckno Black Island Point and Lough Muckno Water Sports Area on the same date did not show the same levels.
Monaghan County Council says to reduce the risk of illness, users should take the following precautions.
The local authority is advising people not to swallow or splash water; wash hands before handling food; avoid swimming with an open cut or wound; and don't swim if pregnant or have a weakened immune system.
Local Councillor Aidan Campbell says that higher levels of bacteria are usually short-lived and he remains hopeful that further samples will result in the warning being lifted.
