It happened yesterday evening
The man had been swimming at the Ballyhass Lakes Activity centre shortly before 5pm yesterday when he lost control and emergency services were contacted.
The Coast Guard helicopter Rescue 115 attended the scene along with an off-duty paramedic.
It's understood the man was administered CPR before being taken to CUH in a critical condition.
In a separate incident, the Baltimore RNLI volunteer lifeboat have been called out to two medical evacuations at Cape Clear in West Cork over the past 24 hours.
