A spokesperson for Daera said the advice was “intended to protect public health while further information is gathered”.
The National Trust, which manages the beach, said officials from Daera and Northern Ireland Water were at the site on Wednesday carrying out investigations.
A spokesperson said the pollution could potentially be linked to food waste or grease entering the sea via the River Bann, but that the cause had not yet been confirmed.
“We are waiting for Daera Bathing Water to carry out sample testing and we will keep the advice against bathing in place until we know that the water is clear,” the spokesperson said.
The temporary notice will remain in place while water samples are analysed and investigations continue.