Dun Laoghaire and Rathdown County Council says the bathing ban in the area has been extended to Seapoint.
Earlier, the council enforced a prohibition notice on swimming in Killiney and Blackrock.
The temporary order was put in place after samples showed high levels of E. Coli and Enterococci bacteria.
Swimmers are now also being advised against swimming at Seapoint.
The order is in place until this coming Monday, July 3rd.
Local Fianna Fáil councillor Cormac Devlin urged people to not let dogs into the water.
Lab results this evening confirm elevated readings for E.coli at between Seapoint & Killiney, dont swim or let dogs in the water over w/end pic.twitter.com/izX5FqXFi7
— Cllr. Cormac Devlin (@CormacDevlin) June 30, 2017