Galway City Council has issued prior warning notices for Grattan and Ballyloughane beaches due to anticipated bacteria levels.
Increased rain forecast for the coming days, and the possibility of storm overflows being activated, could lead to elevated bacteria levels.
The tail end of tropical storm Alex is expected to bring heavy wind and rain over the weekend, though no weather warnings have been issued by Met Eireann as of yet.
Warning notices have been erected at both beaches as of today, and the warning is expected to last until Monday, June 13.
The city council has said that an update will be provided next Wednesday evening, after the results of further water sample tests are received.
In the meantime, anyone visiting Grattan and Ballyloughane beaches is advised to avoid splashing or swallowing any water.
People should also avoid swimming if they have any open wounds, or are pregnant, and to wash their hands before preparing food if they have been in the water.