Water Safety Ireland has issued an appeal for people not to overestimate their swimming ability when swimming outdoors.
The call comes after 50-year-old Desmond Byrne and his 62-year-old sister Muriel Eriksson died in a drowning incident in Co Kerry yesterday.
Speaking on RTÉ's News at One, acting chief executive of Water Safety Ireland Roger Sweeney said that the situation can change in seconds, especially if there is a potential danger of a rip current.
"You may be a good swimmer in the lanes of a swimming pool but that doesn't translate into outdoor swimming.
"You have to think of currents, the water in a hotel pool is much warmer than the open water where your muscles won’t be as effective, especially in fresh water and lakes.
"Be able to stand up so you can literally walk to shore if you get into trouble," he said.
Mr Sweeney recommended making noise and calling for help if you find yourself in difficultly, adding that drowning can often be silent
"Drowning isn't the loud splashing call for help that we see on TV. We shouldn’t fear the water, we should have a healthy respect for the water.
"Children, no more than adults, will enjoy open waters and grow up with respect once they know the dangers," he said.
He recommended that people remember to swim parallel to the shore at a slight angle so that they can get out of the current quickly.
He added that supervision is vital, particularly with children, but also adults who are out with their friends when alcohol or drugs might be a factor.
Should you get into difficulty or see someone else in trouble, dial 999 or 112 and ask for the Coast Guard.