Gardaí are at the scene of an incident at Hollywood Lake in Co Monaghan.
Emergency services are also at the scene, where a man was taken from the water in a serious condition.
He has been transferred to hospital by air ambulance and gardaí have said inquiries are ongoing.
It is the latest incident in Irish waters this week as people flocked to beaches and lakes to enjoy the fine weather.
There have been six drowning incidents this week including a man in his 60s at Dollymount in Dublin last Friday.
The incident occurred when the body was recovered at around 1.30pm that afternoon.
He was pronounced deceased at the scene. His body has been removed to Dublin City Mortuary for post mortem.
Elsewhere, mourners at the funeral today heard how a young mother loved her children after she drowned attempting to rescue her son from a Co Cavan lake.
The latest incident has occurred on what marks the first World Drowning Prevention Day.
On average 115 people die every year in Irish waters, with six drownings this week alone.
In a statement today, the President Michael D Higgins urged everyone to "respect the water and never underestimate its strength".
"On this World Drowning Prevention Day, I urge all of you to respect the water, to never underestimate its strength, and to avoid taking the unnecessary risks that can so easily lead to tragedy, loss and heartbreak," said Mr Higgins.
The RNLI has said Ireland needs to prioritise reducing deaths by drowning in the same manner road fatalities have been tackled.
Lisa Hollingham from the RNLI said it is important to have an annual recognition day in order to reduce water fatalities.
"So today being World Drowning Prevention Day means that the world has accepted that drowning is a real issue, and that nationally and internationally we can put prevention in place to reduce the number of drownings.
"There has been a number of tragedies this week and those families are certainly suffering and our thoughts are with them.
"And it makes it more poignant about today and how we can try and bring those numbers down," she said.