Rescue chiefs have urged youngsters to take extra care when swimming during the heatwave after a spate of tragedies.
The RNLI said it would be stepping up vigilance around Ireland's waterways as people look to cool down in the summer heat.
Four young people have drowned already in accidents in the past few days.
Kevin Rahill, sea safety manager of the RNLI, urged sun-seekers to make sure they can swim properly before getting into the water and to make themselves aware of any particular dangers.
He said: "Generally speaking, we would warn people against swimming in strong currents and strong tides, especially rip tides. If not sure, ask somebody."
Mr Rahill said different waterways will have different dangers. He also warned against jumping off rocks or pier walls unless swimmers are certain there is enough water below them and no submerged obstacles.
The RNLI run a SAFE campaign which reminds swimmers to Spot the dangers; Always go with a friend; Find the flags, and swim in a lifeguard-monitored zone; and heed any Emergency, raise the alarm and contact rescue services.
Mr Rahill also warned against people risking undertaking a rescue themselves unless they are sure they are able, as this can often turn into another casualty.
In the latest incident, a 19-year-old died after getting into difficulty in Annaghmore Lake, near Strokestown, Co Roscommon, on Thursday night.
A 12-year-old boy drowned while swimming at Youghal in Co Cork on Thursday. On Wednesday, a 17-year-old boy in Co Kildare and a 21-year-old woman in Co Limerick also died in separate swimming accidents.