Cork County Council has advised against swimming in seven beaches in the county due to concerns about levels of the E.coli bacteria in the water.
Three of the affected beaches, Redbarn in Youghal, Garretstown near Kinsale and Garryvoe near Castlemartyr, are Blue Flag designated.
The Front Strand and Claycastle in Youghal, Coolmaine near Kilbrittain and Oysterhaven have also been closed.
The closures are a precautionary measure until the quality has been restored.
The levels of bacteria found, which can cause food poisoning, are said to exceed EU permitted guidelines.
The council said the Health Service Executive and the Environmental Protection Agency have been contacted.
It said the beaches are to be re-sampled on Monday as it is felt possible weather related factors have not yet passed.